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/klauspost/cpuid/v2/detect_x86.go

@@ -0,0 +1,45 @@
+// Copyright (c) 2015 Klaus Post, released under MIT License. See LICENSE file.
+
+//go:build (386 && !gccgo && !noasm && !appengine) || (amd64 && !gccgo && !noasm && !appengine)
+// +build 386,!gccgo,!noasm,!appengine amd64,!gccgo,!noasm,!appengine
+
+package cpuid
+
+func asmCpuid(op uint32) (eax, ebx, ecx, edx uint32)
+func asmCpuidex(op, op2 uint32) (eax, ebx, ecx, edx uint32)
+func asmXgetbv(index uint32) (eax, edx uint32)
+func asmRdtscpAsm() (eax, ebx, ecx, edx uint32)
+func asmDarwinHasAVX512() bool
+
+func initCPU() {
+	cpuid = asmCpuid
+	cpuidex = asmCpuidex
+	xgetbv = asmXgetbv
+	rdtscpAsm = asmRdtscpAsm
+	darwinHasAVX512 = asmDarwinHasAVX512
+}
+
+func addInfo(c *CPUInfo, safe bool) {
+	c.maxFunc = maxFunctionID()
+	c.maxExFunc = maxExtendedFunction()
+	c.BrandName = brandName()
+	c.CacheLine = cacheLine()
+	c.Family, c.Model, c.Stepping = familyModel()
+	c.featureSet = support()
+	c.SGX = hasSGX(c.featureSet.inSet(SGX), c.featureSet.inSet(SGXLC))
+	c.AMDMemEncryption = hasAMDMemEncryption(c.featureSet.inSet(SME) || c.featureSet.inSet(SEV))
+	c.ThreadsPerCore = threadsPerCore()
+	c.LogicalCores = logicalCores()
+	c.PhysicalCores = physicalCores()
+	c.VendorID, c.VendorString = vendorID()
+	c.HypervisorVendorID, c.HypervisorVendorString = hypervisorVendorID()
+	c.AVX10Level = c.supportAVX10()
+	c.cacheSize()
+	c.frequencies()
+	if c.maxFunc >= 0x0A {
+		eax, ebx, _, edx := cpuid(0x0A)
+		c.PMU = parseLeaf0AH(c, eax, ebx, edx)
+	}
+}
+
+func getVectorLength() (vl, pl uint64) { return 0, 0 }