Add unit tests + CI for the password hasher

[royashbrook]

Context

The test/ folder had a stub Tests.cs.txt (disabled — note the .txt extension) that asserted deterministic outputs from the non-deterministic HashPassword method. Couldn't have ever passed.

Need real tests so future contributors get a green/red signal.

Done in PR #1

• xUnit project under test/h.Tests/ that compiles the vendored PasswordHasher.cs directly (avoids ProjectReference-on-Exe awkwardness)
• 21 tests covering:
  • Format/shape: 84-char base64, v3 marker prefix, salts vary across calls
  • Roundtrip: HashPassword + VerifyHashedPassword succeed across ASCII / symbols / unicode passwords
  • Wrong password fails, empty provided password fails
  • Known-good regression fixtures: pre-computed (password, hash) pairs that must always verify
  • Tampered hashes fail (suffix-mangled known hashes, must verify False)
  • Cross-tool compat: a hash minted by frtl/frtl-bc/scripts/Get-PasswordHash.ps1 (pure pwsh, same v3 byte format) must verify against this build — pins the wire format as a public contract
• .github/workflows/ci.yml runs dotnet test on push to main and on every PR

Local result: Passed! - Failed: 0, Passed: 21, Skipped: 0, Total: 21

Out of scope

• Modernizing crypto defaults (the vendored hasher uses HMAC-SHA256 / 10000 iter; current ASP.NET Identity defaults to SHA512 / 100000). Behavior preserved deliberately. If we do upgrade, the regression fixtures here would need updating — but Verify still accepts both formats so existing hashes would not break.
• A Dockerfile or other distribution beyond the existing dist.sh single-file publish.

Related

• frtl/frtl-bc uses the format this tool produces — verifies migrated bcv2 hashes via the same PasswordHasher.VerifyHashedPassword path.
• frtl/frtl-bc has a scripts/Get-PasswordHash.ps1 that produces the same v3 format in pure pwsh, used as the day-to-day admin tool. This CLI is the reference verifier.

[royashbrook]

Done in PR #1 (squash-merged into master) + small follow-up fix in 173b88a (excludes test/** from greedy globbing in h.csproj). Released as v1.1.0: https://github.com/royashbrook/CLI-PasswordHasher/releases/tag/v1.1.0