fix: bootstrap V on Windows with makev.bat

[ulises-jeremias]

Summary

• On Windows, bootstrap V with makev.bat -gcc instead of GNU make, matching vlang/v CI and official Windows install docs.
• Detect v.exe for install checks, rebuilds, version probing, and action outputs.
• If the install directory exists but the executable is missing (failed prior run), remove it and re-download instead of returning early.
• Resolve the latest GitHub release when stable: true, even without check-latest: true (fixes confusing behavior documented in The action starts to fail to setup stable version with error: unknown function: help.print_and_exit #3).
• Add unit tests for executable path resolution and version ref logic.

Fixes #16

Context

This addresses Windows bootstrap failures tracked in #15 (MinGW/POSIX headers when running make on master) and the stable-only scenario used by downstream projects (e.g. VSL/VTL Windows smoke jobs with stable: true + check-latest: true).

Test plan

• npm run all (build, lint, package, vitest) passes locally
• CI test-action matrix on ubuntu/windows/macos (check-latest, stable, version scenarios)
• Check dist workflow passes with updated dist/index.js

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