test: assert DI extension wiring and provider key normalization invariant

[turegjorup]

Summary

First of four scoped follow-ups to #44 killing surviving mutants to push the mutation score above 90%. This PR covers src/DependencyInjection (8 escaped mutants — the largest single cluster).

Features Added

• ItkDevOpenIdConnectExtensionTest: two new tests asserting the container wiring the extension performs — the cacheItemPool Reference on the provider manager config, the provider options mapping (keyed by provider name, options level stripped), and the $cache/$cliLoginRoute arguments on CliLoginHelper, UserLoginCommand and CliLoginTokenAuthenticator. Previously only hasDefinition() was checked, so every replaceArgument() call could be deleted without a failing test.
• ConfigurationTest: test for the documented invariant that provider keys are not normalized (my-provider and my_provider are distinct providers) — normalizeKeys(false) could be flipped to true undetected.

Files Changed

• tests/DependencyInjection/ItkDevOpenIdConnectExtensionTest.php - wiring assertions
• tests/DependencyInjection/ConfigurationTest.php - key normalization test
• CHANGELOG.md - Unreleased bullet

Test Plan

• vendor/bin/phpunit — 82 tests, 182 assertions, green
• vendor/bin/infection --filter=src/DependencyInjection — 20/20 mutants killed (was 12/20)
• PHPStan max level + php-cs-fixer — clean

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (25afc4c) to head (a03ca2d).

Additional details and impacted files

@@             Coverage Diff             @@
##             develop       #45   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        62        62           
===========================================
  Files              9         9           
  Lines            282       282           
===========================================
  Hits             282       282           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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