Insuffiect material draw and Perft testing

[Mgrdich]

No description provided.

[Copilot]

Pull request overview

This pull request implements insufficient material draw detection and perft (performance test) validation for the chess engine. It completes Slices 13 and 14 of the chess engine foundation specification.

Key Changes:

• Implements insufficient material draw detection that automatically ends games when neither side can force checkmate (K vs K, K+B vs K, K+N vs K, K+B vs K+B with same-color bishops)
• Adds perft testing functionality to validate move generation correctness against known benchmark positions
• Implements FEN (Forsyth-Edwards Notation) parsing to create board positions from standard chess notation

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
internal/engine/game_state.go	Implements insufficient material detection logic with material counting and automatic draw status
internal/engine/game_state_test.go	Comprehensive test suite for all insufficient material scenarios (K vs K, K+B vs K, K+N vs K, same-color bishops, etc.)
internal/engine/board.go	Adds Perft and Divide methods for performance testing and debugging move generation
internal/engine/perft_test.go	Test suite with known perft positions including starting position, kiwipete, and other standard benchmarks
internal/engine/fen.go	FEN parser implementation with validation for piece placement, castling rights, en passant, and move counters
internal/engine/fen_test.go	Tests for FEN parsing including valid positions, error cases, and specific FEN components
context/spec/001-chess-engine-foundation/tasks.md	Marks Slices 13 and 14 as complete
context/spec/001-chess-engine-foundation/functional-spec.md	Table formatting improvements for special rules section

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