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_arm64.go

@@ -28,6 +28,7 @@ func initOptions() {
 		{Name: "sm3", Feature: &ARM64.HasSM3},
 		{Name: "sm4", Feature: &ARM64.HasSM4},
 		{Name: "sve", Feature: &ARM64.HasSVE},
+		{Name: "sve2", Feature: &ARM64.HasSVE2},
 		{Name: "crc32", Feature: &ARM64.HasCRC32},
 		{Name: "atomics", Feature: &ARM64.HasATOMICS},
 		{Name: "asimdhp", Feature: &ARM64.HasASIMDHP},
@@ -37,6 +38,8 @@ func initOptions() {
 		{Name: "dcpop", Feature: &ARM64.HasDCPOP},
 		{Name: "asimddp", Feature: &ARM64.HasASIMDDP},
 		{Name: "asimdfhm", Feature: &ARM64.HasASIMDFHM},
+		{Name: "dit", Feature: &ARM64.HasDIT},
+		{Name: "i8mm", Feature: &ARM64.HasI8MM},
 	}
 }
 
@@ -44,7 +47,7 @@ func archInit() {
 	switch runtime.GOOS {
 	case "freebsd":
 		readARM64Registers()
-	case "linux", "netbsd", "openbsd":
+	case "linux", "netbsd", "openbsd", "windows":
 		doinit()
 	default:
 		// Many platforms don't seem to allow reading these registers.
@@ -144,6 +147,11 @@ func parseARM64SystemRegisters(isar0, isar1, pfr0 uint64) {
 		ARM64.HasLRCPC = true
 	}
 
+	switch extractBits(isar1, 52, 55) {
+	case 1:
+		ARM64.HasI8MM = true
+	}
+
 	// ID_AA64PFR0_EL1
 	switch extractBits(pfr0, 16, 19) {
 	case 0:
@@ -164,6 +172,20 @@ func parseARM64SystemRegisters(isar0, isar1, pfr0 uint64) {
 	switch extractBits(pfr0, 32, 35) {
 	case 1:
 		ARM64.HasSVE = true
+
+		parseARM64SVERegister(getzfr0())
+	}
+
+	switch extractBits(pfr0, 48, 51) {
+	case 1:
+		ARM64.HasDIT = true
+	}
+}
+
+func parseARM64SVERegister(zfr0 uint64) {
+	switch extractBits(zfr0, 0, 3) {
+	case 1:
+		ARM64.HasSVE2 = true
 	}
 }