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/pjbgf/sha1cd/sha1cd.go

@@ -38,8 +38,7 @@ type digest struct {
 	len uint64
 
 	// col defines whether a collision has been found.
-	col       bool
-	blockFunc func(dig *digest, p []byte)
+	col bool
 }
 
 func (d *digest) MarshalBinary() ([]byte, error) {
@@ -99,7 +98,7 @@ func (d *digest) UnmarshalBinary(b []byte) error {
 
 func consumeUint64(b []byte) ([]byte, uint64) {
 	_ = b[7]
-	x := uint64(b[7]) | uint64(b[6])<<8 | uint64(b[shared.WordBuffers])<<16 | uint64(b[4])<<24 |
+	x := uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
 		uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
 	return b[8:], x
 }
@@ -126,21 +125,9 @@ func (d *digest) Reset() {
 // implements encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to
 // marshal and unmarshal the internal state of the hash.
 func New() hash.Hash {
-	d := new(digest)
-
-	d.blockFunc = block
+	var d digest
 	d.Reset()
-	return d
-}
-
-// NewGeneric is equivalent to New but uses the Go generic implementation,
-// avoiding any processor-specific optimizations.
-func NewGeneric() hash.Hash {
-	d := new(digest)
-
-	d.blockFunc = blockGeneric
-	d.Reset()
-	return d
+	return &d
 }
 
 func (d *digest) Size() int { return Size }
@@ -158,14 +145,14 @@ func (d *digest) Write(p []byte) (nn int, err error) {
 		n := copy(d.x[d.nx:], p)
 		d.nx += n
 		if d.nx == shared.Chunk {
-			d.blockFunc(d, d.x[:])
+			block(d, d.x[:])
 			d.nx = 0
 		}
 		p = p[n:]
 	}
 	if len(p) >= shared.Chunk {
 		n := len(p) &^ (shared.Chunk - 1)
-		d.blockFunc(d, p[:n])
+		block(d, p[:n])
 		p = p[n:]
 	}
 	if len(p) > 0 {
@@ -184,18 +171,20 @@ func (d *digest) Sum(in []byte) []byte {
 func (d *digest) checkSum() [Size]byte {
 	len := d.len
 	// Padding.  Add a 1 bit and 0 bits until 56 bytes mod 64.
-	var tmp [64]byte
+	var tmp [64 + 8]byte
 	tmp[0] = 0x80
+	var t uint64
 	if len%64 < 56 {
-		d.Write(tmp[0 : 56-len%64])
+		t = 56 - len%64
 	} else {
-		d.Write(tmp[0 : 64+56-len%64])
+		t = 64 + 56 - len%64
 	}
 
 	// Length in bits.
 	len <<= 3
-	binary.BigEndian.PutUint64(tmp[:], len)
-	d.Write(tmp[0:8])
+	padlen := tmp[:t+8]
+	binary.BigEndian.PutUint64(tmp[t:], len)
+	d.Write(padlen)
 
 	if d.nx != 0 {
 		panic("d.nx != 0")
@@ -214,7 +203,8 @@ func (d *digest) checkSum() [Size]byte {
 
 // Sum returns the SHA-1 checksum of the data.
 func Sum(data []byte) ([Size]byte, bool) {
-	d := New().(*digest)
+	var d digest
+	d.Reset()
 	d.Write(data)
 	return d.checkSum(), d.col
 }