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.s

@@ -9,23 +9,27 @@
 // func getisar0() uint64
 TEXT ·getisar0(SB),NOSPLIT,$0-8
 	// get Instruction Set Attributes 0 into x0
-	// mrs x0, ID_AA64ISAR0_EL1 = d5380600
-	WORD	$0xd5380600
+	MRS	ID_AA64ISAR0_EL1, R0
 	MOVD	R0, ret+0(FP)
 	RET
 
 // func getisar1() uint64
 TEXT ·getisar1(SB),NOSPLIT,$0-8
 	// get Instruction Set Attributes 1 into x0
-	// mrs x0, ID_AA64ISAR1_EL1 = d5380620
-	WORD	$0xd5380620
+	MRS	ID_AA64ISAR1_EL1, R0
 	MOVD	R0, ret+0(FP)
 	RET
 
 // func getpfr0() uint64
 TEXT ·getpfr0(SB),NOSPLIT,$0-8
 	// get Processor Feature Register 0 into x0
-	// mrs x0, ID_AA64PFR0_EL1 = d5380400
-	WORD	$0xd5380400
+	MRS	ID_AA64PFR0_EL1, R0
+	MOVD	R0, ret+0(FP)
+	RET
+
+// func getzfr0() uint64
+TEXT ·getzfr0(SB),NOSPLIT,$0-8
+	// get SVE Feature Register 0 into x0
+	MRS	ID_AA64ZFR0_EL1, R0
 	MOVD	R0, ret+0(FP)
 	RET