chore: modernize CI and update Go toolchain

- Bump Go from 1.19 to 1.26 and update all dependencies
- Rewrite CI workflow with matrix strategy (Linux, macOS, Windows)
- Update GitHub Actions to current versions (checkout@v4, setup-go@v5)
- Update CodeQL actions from v1 to v3
- Fix cross-platform bug in mock/path.go (path.Join -> filepath.Join)
- Clean up dependabot config (weekly schedule, remove stale ignore)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vendor/github.com/cloudflare/circl/dh/x25519/curve_amd64.s

@@ -1,4 +1,5 @@
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 #include "textflag.h"
 

vendor/github.com/cloudflare/circl/dh/x448/curve_amd64.s

@@ -1,4 +1,5 @@
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 #include "textflag.h"
 

vendor/github.com/cloudflare/circl/ecc/goldilocks/curve.go

@@ -18,6 +18,9 @@ func (Curve) Identity() *Point {
 func (Curve) IsOnCurve(P *Point) bool {
 	x2, y2, t, t2, z2 := &fp.Elt{}, &fp.Elt{}, &fp.Elt{}, &fp.Elt{}, &fp.Elt{}
 	rhs, lhs := &fp.Elt{}, &fp.Elt{}
+	// Check z != 0
+	eq0 := !fp.IsZero(&P.z)
+
 	fp.Mul(t, &P.ta, &P.tb)  // t = ta*tb
 	fp.Sqr(x2, &P.x)         // x^2
 	fp.Sqr(y2, &P.y)         // y^2
@@ -27,13 +30,14 @@ func (Curve) IsOnCurve(P *Point) bool {
 	fp.Mul(rhs, t2, &paramD) // dt^2
 	fp.Add(rhs, rhs, z2)     // z^2 + dt^2
 	fp.Sub(lhs, lhs, rhs)    // x^2 + y^2 - (z^2 + dt^2)
-	eq0 := fp.IsZero(lhs)
+	eq1 := fp.IsZero(lhs)
 
 	fp.Mul(lhs, &P.x, &P.y) // xy
 	fp.Mul(rhs, t, &P.z)    // tz
 	fp.Sub(lhs, lhs, rhs)   // xy - tz
-	eq1 := fp.IsZero(lhs)
-	return eq0 && eq1
+	eq2 := fp.IsZero(lhs)
+
+	return eq0 && eq1 && eq2
 }
 
 // Generator returns the generator point.

vendor/github.com/cloudflare/circl/internal/conv/conv.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"math/big"
 	"strings"
+
+	"golang.org/x/crypto/cryptobyte"
 )
 
 // BytesLe2Hex returns an hexadecimal string of a number stored in a
@@ -138,3 +140,34 @@ func BigInt2Uint64Le(z []uint64, x *big.Int) {
 		z[i] = 0
 	}
 }
+
+// MarshalBinary encodes a value into a byte array in a format readable by UnmarshalBinary.
+func MarshalBinary(v cryptobyte.MarshalingValue) ([]byte, error) {
+	const DefaultSize = 32
+	b := cryptobyte.NewBuilder(make([]byte, 0, DefaultSize))
+	b.AddValue(v)
+	return b.Bytes()
+}
+
+// MarshalBinaryLen encodes a value into an array of n bytes in a format readable by UnmarshalBinary.
+func MarshalBinaryLen(v cryptobyte.MarshalingValue, length uint) ([]byte, error) {
+	b := cryptobyte.NewFixedBuilder(make([]byte, 0, length))
+	b.AddValue(v)
+	return b.Bytes()
+}
+
+// A UnmarshalingValue decodes itself from a cryptobyte.String and advances the pointer.
+// It reports whether the read was successful.
+type UnmarshalingValue interface {
+	Unmarshal(*cryptobyte.String) bool
+}
+
+// UnmarshalBinary recovers a value from a byte array.
+// It returns an error if the read was unsuccessful.
+func UnmarshalBinary(v UnmarshalingValue, data []byte) (err error) {
+	s := cryptobyte.String(data)
+	if data == nil || !v.Unmarshal(&s) || !s.Empty() {
+		err = fmt.Errorf("cannot read %T from input string", v)
+	}
+	return
+}

vendor/github.com/cloudflare/circl/internal/sha3/xor_unaligned.go

@@ -14,14 +14,14 @@ import "unsafe"
 type storageBuf [maxRate / 8]uint64
 
 func (b *storageBuf) asBytes() *[maxRate]byte {
-	return (*[maxRate]byte)(unsafe.Pointer(b))
+	return (*[maxRate]byte)(unsafe.Pointer(b)) //nolint:gosec
 }
 
 // xorInuses unaligned reads and writes to update d.a to contain d.a
 // XOR buf.
 func xorIn(d *State, buf []byte) {
 	n := len(buf)
-	bw := (*[maxRate / 8]uint64)(unsafe.Pointer(&buf[0]))[: n/8 : n/8]
+	bw := (*[maxRate / 8]uint64)(unsafe.Pointer(&buf[0]))[: n/8 : n/8] //nolint:gosec
 	if n >= 72 {
 		d.a[0] ^= bw[0]
 		d.a[1] ^= bw[1]
@@ -56,6 +56,6 @@ func xorIn(d *State, buf []byte) {
 }
 
 func copyOut(d *State, buf []byte) {
-	ab := (*[maxRate]uint8)(unsafe.Pointer(&d.a[0]))
+	ab := (*[maxRate]uint8)(unsafe.Pointer(&d.a[0])) //nolint:gosec
 	copy(buf, ab[:])
 }

vendor/github.com/cloudflare/circl/math/fp25519/fp_amd64.s

@@ -1,4 +1,5 @@
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 #include "textflag.h"
 #include "fp_amd64.h"

vendor/github.com/cloudflare/circl/math/fp448/fp_amd64.s

@@ -1,4 +1,5 @@
-// +build amd64
+//go:build amd64 && !purego
+// +build amd64,!purego
 
 #include "textflag.h"
 #include "fp_amd64.h"

vendor/github.com/cloudflare/circl/math/integer.go

@@ -0,0 +1,16 @@
+package math
+
+import "math/bits"
+
+// NextPow2 finds the next power of two (N=2^k, k>=0) greater than n.
+// If n is already a power of two, then this function returns n, and log2(n).
+func NextPow2(n uint) (N uint, k uint) {
+	if bits.OnesCount(n) == 1 {
+		k = uint(bits.TrailingZeros(n))
+		N = n
+	} else {
+		k = uint(bits.Len(n))
+		N = uint(1) << k
+	}
+	return
+}

vendor/github.com/cloudflare/circl/sign/ed25519/point.go

@@ -164,7 +164,7 @@ func (P *pointR1) isEqual(Q *pointR1) bool {
 	fp.Mul(r, r, &P.z)
 	fp.Sub(l, l, r)
 	b = b && fp.IsZero(l)
-	return b
+	return b && !fp.IsZero(&P.z) && !fp.IsZero(&Q.z)
 }
 
 func (P *pointR3) neg() {

vendor/github.com/cloudflare/circl/sign/ed448/ed448.go

@@ -206,7 +206,7 @@ func newKeyFromSeed(privateKey, seed []byte) {
 
 func signAll(signature []byte, privateKey PrivateKey, message, ctx []byte, preHash bool) {
 	if len(ctx) > ContextMaxSize {
-		panic(fmt.Errorf("ed448: bad context length: " + strconv.Itoa(len(ctx))))
+		panic(fmt.Errorf("ed448: bad context length: %v", len(ctx)))
 	}
 
 	H := sha3.NewShake256()

vendor/github.com/cloudflare/circl/sign/sign.go

@@ -38,6 +38,12 @@ type PrivateKey interface {
 	encoding.BinaryMarshaler
 }
 
+// A private key that retains the seed with which it was generated.
+type Seeded interface {
+	// returns the seed if retained, otherwise nil
+	Seed() []byte
+}
+
 // A Scheme represents a specific instance of a signature scheme.
 type Scheme interface {
 	// Name of the scheme.
@@ -107,4 +113,7 @@ var (
 	// ErrContextNotSupported is the error used if a context is not
 	// supported.
 	ErrContextNotSupported = errors.New("context not supported")
+
+	// ErrContextTooLong is the error used if the context string is too long.
+	ErrContextTooLong = errors.New("context string too long")
 )