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_riscv64.go

@@ -8,4 +8,25 @@ package cpu
 
 const cacheLineSize = 64
 
-func initOptions() {}
+func initOptions() {
+	options = []option{
+		{Name: "fastmisaligned", Feature: &RISCV64.HasFastMisaligned},
+		{Name: "c", Feature: &RISCV64.HasC},
+		{Name: "v", Feature: &RISCV64.HasV},
+		{Name: "zba", Feature: &RISCV64.HasZba},
+		{Name: "zbb", Feature: &RISCV64.HasZbb},
+		{Name: "zbs", Feature: &RISCV64.HasZbs},
+		// RISC-V Cryptography Extensions
+		{Name: "zvbb", Feature: &RISCV64.HasZvbb},
+		{Name: "zvbc", Feature: &RISCV64.HasZvbc},
+		{Name: "zvkb", Feature: &RISCV64.HasZvkb},
+		{Name: "zvkg", Feature: &RISCV64.HasZvkg},
+		{Name: "zvkt", Feature: &RISCV64.HasZvkt},
+		{Name: "zvkn", Feature: &RISCV64.HasZvkn},
+		{Name: "zvknc", Feature: &RISCV64.HasZvknc},
+		{Name: "zvkng", Feature: &RISCV64.HasZvkng},
+		{Name: "zvks", Feature: &RISCV64.HasZvks},
+		{Name: "zvksc", Feature: &RISCV64.HasZvksc},
+		{Name: "zvksg", Feature: &RISCV64.HasZvksg},
+	}
+}