Feature/volt phase1

[niden]

Summary

This PR delivers Phase 1 of the Volt parser modernisation effort: replacing loose, C-style PHP with idiomatic PHP 8.1+ constructs, encapsulating internal state, and establishing a comprehensive unit test suite.

What changed

Scanner layer

• Opcode converted to a backed enum (int cases) — replaces 70+ bare integer constants
• Token converted to a readonly class with constructor promotion — immutable value object
• ScannerStatus introduced as a typed enum for scanner result codes (replacing raw integers)
• State fully encapsulated: all public properties replaced with protected/private and accessor methods (get*, set*, increment*, decrement*, reset*)
• Scanner updated to use all new accessors

Parser layer

• Parser updated to use State accessors throughout; $state->setActiveToken(null) for typed nullable reset
• Parser\Status properties tightened to private; constructor-promoted; setter return types corrected
• resources/files/parser.php (lemon-generated) updated to use State getter methods for EOF error reporting

Exception

• $statement property added with getStatement(): array accessor to carry the failing AST node alongside the message

Infrastructure

• Tokens.php: null array key replaced with '' (PHP 8.5 compatibility)
• phpstan-baseline.neon: PHP 8.5-only Compiler.php errors suppressed with reportUnmatched: false so 8.1–8.4 runs are unaffected
• GitHub Actions workflow updated: coverage: none for phpcs job, coverage: xdebug for tests/coverage jobs, Codecov file: → files:
• Docker environment updated with PHP 8.1–8.5 images and matching docker-compose.yml

Test coverage added

File	Tests
tests/unit/Scanner/OpcodeTest.php	Opcode enum — all cases, fromOpcode(), label lookup
tests/unit/Scanner/TokenTest.php	Token value object — all properties, readonly enforcement
tests/unit/Scanner/ScannerStatusTest.php	ScannerStatus enum — all cases
tests/unit/Scanner/StateTest.php	State — all getters/setters/incrementers
tests/unit/Parser/StatusTest.php	Parser\Status — all methods and constants
tests/unit/ExceptionTest.php	Exception — message, statement, code
tests/unit/Parser/ParserTest.php	Parser — 37 tests covering every statement type, error path, and extends-mode restriction

31 files changed, ~3 000 lines added, ~840 removed.

Test plan

• composer cs passes on PHP 8.1–8.5
• composer analyze passes on PHP 8.1–8.5
• composer test passes (372 tests, 3 intentional skips for Phase 2 Compiler work)
• CI green on all matrix entries

[codecov]

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