Fixes #5638. Scope ANSI key deduplication

[YourRobotOverlord]

Summary

Revert the timing-based printable suppression from #5618 and replace it with protocol-aware, batch-scoped deduplication.

• Fixes ANSI printable-suppression window swallows real Tab within 50ms of Shift+Tab #5638

Changes

• preserve the ANSI parser pattern that recognized each key event
• arm parsed-key suppression only for KittyKeyboardPattern, so legacy ESC[Z Shift+Tab cannot suppress a following Tab
• retain Some keys print twice in the terminal on Windows with kitty enabled #4918 fallback-only deduplication for kitty-enabled input when both duplicate characters arrive in one processing batch
• clear all suppression candidates when that batch ends, preserving separate repeated legacy keypresses from Kitty-enabled ANSI input drops every second repeated legacy key #5616
• remove the 50 ms suppression timeout and its stale cross-event matching

The ANSI character stream has no physical-key identity. Consequently, duplicate halves split across separate processing batches are delivered separately; this is the deterministic tradeoff for avoiding a timing heuristic.

Testing

• dotnet build --no-restore
• dotnet test --project Tests/UnitTestsParallelizable --no-build --filter-class "*KittyKeyboardPipelineTests" — 108 passed
• AnsiResponseParserTests — 59 passed
• InputProcessorImplTests — 31 passed, 1 pre-existing skip
• dotnet test --project Tests/UnitTests.NonParallelizable --no-build — 72 passed, 2 pre-existing skips
• dotnet test --project Tests/IntegrationTests --no-build — 437 passed
• full parallelizable suite — 17,579 passed, 17 skipped; four unrelated terminal-color expectation failures reproduced on the comparison branch, plus one global-state test that passed in isolation

To pull down this PR locally:

git remote add yourrobotoverlord https://github.com/YourRobotOverlord/Terminal.Gui.git
git fetch yourrobotoverlord fix/5638-revert-5618-reimpl-dedup
git checkout yourrobotoverlord/fix/5638-revert-5618-reimpl-dedup