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/golang.org/x/sys/cpu/cpu.go

@@ -72,6 +72,9 @@ var X86 struct {
 	HasSSSE3            bool // Supplemental streaming SIMD extension 3
 	HasSSE41            bool // Streaming SIMD extension 4 and 4.1
 	HasSSE42            bool // Streaming SIMD extension 4 and 4.2
+	HasAVXIFMA          bool // Advanced vector extension Integer Fused Multiply Add
+	HasAVXVNNI          bool // Advanced vector extension Vector Neural Network Instructions
+	HasAVXVNNIInt8      bool // Advanced vector extension Vector Neural Network Int8 instructions
 	_                   CacheLinePad
 }
 
@@ -103,7 +106,10 @@ var ARM64 struct {
 	HasASIMDDP  bool // Advanced SIMD double precision instruction set
 	HasSHA512   bool // SHA512 hardware implementation
 	HasSVE      bool // Scalable Vector Extensions
+	HasSVE2     bool // Scalable Vector Extensions 2
 	HasASIMDFHM bool // Advanced SIMD multiplication FP16 to FP32
+	HasDIT      bool // Data Independent Timing support
+	HasI8MM     bool // Advanced SIMD Int8 matrix multiplication instructions
 	_           CacheLinePad
 }
 
@@ -143,6 +149,18 @@ var ARM struct {
 	_           CacheLinePad
 }
 
+// The booleans in Loong64 contain the correspondingly named cpu feature bit.
+// The struct is padded to avoid false sharing.
+var Loong64 struct {
+	_         CacheLinePad
+	HasLSX    bool // support 128-bit vector extension
+	HasLASX   bool // support 256-bit vector extension
+	HasCRC32  bool // support CRC instruction
+	HasLAM_BH bool // support AM{SWAP/ADD}[_DB].{B/H} instruction
+	HasLAMCAS bool // support AMCAS[_DB].{B/H/W/D} instruction
+	_         CacheLinePad
+}
+
 // MIPS64X contains the supported CPU features of the current mips64/mips64le
 // platforms. If the current platform is not mips64/mips64le or the current
 // operating system is not Linux then all feature flags are false.
@@ -198,6 +216,36 @@ var S390X struct {
 	_         CacheLinePad
 }
 
+// RISCV64 contains the supported CPU features and performance characteristics for riscv64
+// platforms. The booleans in RISCV64, with the exception of HasFastMisaligned, indicate
+// the presence of RISC-V extensions.
+//
+// It is safe to assume that all the RV64G extensions are supported and so they are omitted from
+// this structure. As riscv64 Go programs require at least RV64G, the code that populates
+// this structure cannot run successfully if some of the RV64G extensions are missing.
+// The struct is padded to avoid false sharing.
+var RISCV64 struct {
+	_                 CacheLinePad
+	HasFastMisaligned bool // Fast misaligned accesses
+	HasC              bool // Compressed instruction-set extension
+	HasV              bool // Vector extension compatible with RVV 1.0
+	HasZba            bool // Address generation instructions extension
+	HasZbb            bool // Basic bit-manipulation extension
+	HasZbs            bool // Single-bit instructions extension
+	HasZvbb           bool // Vector Basic Bit-manipulation
+	HasZvbc           bool // Vector Carryless Multiplication
+	HasZvkb           bool // Vector Cryptography Bit-manipulation
+	HasZvkt           bool // Vector Data-Independent Execution Latency
+	HasZvkg           bool // Vector GCM/GMAC
+	HasZvkn           bool // NIST Algorithm Suite (AES/SHA256/SHA512)
+	HasZvknc          bool // NIST Algorithm Suite with carryless multiply
+	HasZvkng          bool // NIST Algorithm Suite with GCM
+	HasZvks           bool // ShangMi Algorithm Suite
+	HasZvksc          bool // ShangMi Algorithm Suite with carryless multiplication
+	HasZvksg          bool // ShangMi Algorithm Suite with GCM
+	_                 CacheLinePad
+}
+
 func init() {
 	archInit()
 	initOptions()