Cache xsi:type encoder detection in XsiTypeDetector

[veewee]

Summary

Introduces ScopedCache (src/Cache/ScopedCache.php): a generic, GC-safe WeakMap-based cache scoped to an object's lifetime. When the scope object is garbage collected, all its cached entries are released. Marked @internal.

XsiTypeDetector: caches the full FixedIsoEncoder per (registry, namespace, typeName, meta fingerprint). The meta fingerprint includes isElement, isAttribute, isNullable, isList, and isQualified. This eliminates both encoder detection and iso rebuilding on the decode hot path for repeated xsi:type values.

EncoderDetector: refactored from inline WeakMap to use ScopedCache (same behavior, consistent pattern).

Cache key design

The cache key is namespace|typeName plus a meta fingerprint of 5 bits that affect the encoder's iso() behavior. These were identified by tracing every $meta-> access in encoder iso() methods:

• isElement / isAttribute: read by ErrorHandlingEncoder::iso()
• isNullable: read by ObjectAccess, AnyElementEncoder::iso()
• isList: read by ObjectEncoder::from(), AnyElementEncoder::iso()
• isQualified: read by ElementBuilder (encode path, captured in iso closures)

Other XsdType properties (targetNodeName, targetNamespace) vary per property but only affect the encode direction. Since the cached FixedIsoEncoder is only used for decode (from XsiTypeEncoder::from()), they don't need to be in the key.

Impact

~34% improvement on encoded decode path (113ms to 75ms for 500 items). Literal decode and all encode paths are unaffected.

Test plan

• Full test suite passes (552 tests, 3 new)
• Psalm clean
• CS fixer clean
• Benchmarked against main: -34% decode encoded, no regression elsewhere
• 16 existing ImpliedSchema tests exercise xsi:type with different meta combinations
• 3 new tests: nullable vs non-nullable same xsi:type, separate registries, list vs non-list