Prefer oldspcomp for SourceMod 1.13 builds where spcomp is SourcePawn 2

[Copilot]

SourceMod 1.13.0.7442 is the last pure SP 1.13 compiler build; from 1.13.0.7451 onward, spcomp tracks SourcePawn 2 and breaks legacy code paths (notably VFormat). This change ensures setup-sp selects the SP1-compatible compiler for those builds.

• Version-gated compiler swap (src/installer.ts)

  • Added a targeted gate for 1.13.* with build >= 7451.
  • For matching versions, swaps:
    • oldspcomp -> spcomp
    • oldspcomp64 -> spcomp64
  • Non-matching versions keep existing behavior.

• Preserve SourcePawn 2 compiler binaries

  • Before swap, current compilers are retained as:
    • spcomp_sourcepawn2
    • spcomp64_sourcepawn2
  • Swap is conditional on both old/current binaries existing to avoid unsafe renames.

• Bundled action output update

  • Regenerated lib/index.js to include the installer logic change.

function isSourceMod113Build7451OrLater(version: string): boolean {
  const [major, minor, build] = version.split('.').map(Number);
  return major === 1 && minor === 13 && build >= 7451;
}

• Fixes SM 1.13 compiler builds past 7442 are SourcePawn 2 #40

[rumblefrog]

Closing in favor of #44