feat(diagnostics): detect declare(strict_types=1) for stricter type checking

[calebdw]

Important

Depends on #192

Scans the calling file for declare(strict_types=1) and tightens
argument type checking accordingly. Under strict types, implicit
scalar coercions that PHP normally allows are now flagged:

• int/float → string (TypeError in strict mode)
• numeric-string → int/float (string-to-number coercion forbidden)

The int → float exception is preserved, matching PHP's runtime
semantics. Concatenation (.) is unaffected since it is not a
scalar type declaration context.

The strict_types flag is detected once per file inside the
with_parsed_program closure and threaded through
is_type_compatible to the affected MAYBE rules.

Includes 7 new integration tests covering: int→string flagging,
int→float exception, numeric-string→int flagging, int literal→string,
float→string, concatenation unaffected, and the non-strict baseline.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 57.77778% with 19 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/diagnostics/type_errors.rs	57.77%	19 Missing ⚠️

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