[sql-hkr]

Summary

Closes #43.

This PR implements switch-case-default control flow support in the C compiler:

• Lexer: Added switch, case, default keywords and : punctuation.
• AST: Defined SwitchStmt, CaseClause, and DefaultClause.
• Parser: Implemented parsing of switch statements, multiple case clauses, and default clauses.
• CodeGenerator:
  • Evaluates switch condition once into R16.
  • Sequential dispatch using CPI / BREQ (and CP for non-literal expressions).
  • Emits clause bodies sequentially to support natural C fall-through.
  • Integrates with loop_end_stack so that break exits the switch statement, while preserving outer loop continue behavior.
• Tests: Comprehensive unit tests covering basic dispatch, fall-through, arbitrary default placement, non-literal cases, break/continue inside loops, nested switches, and parser error cases (maintaining 100% test coverage on compiler.py).

Verification

• uv run pytest tests/test_compiler.py --cov=tiny8.compiler --cov-report=term-missing (100% coverage, 65 tests passed)
• uv run pytest (329 tests passed)
• uv run ruff check & uv run ruff format --check (clean)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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