feat: extend key generator with Path, UUID, Decimal, Enum, datetime, and constrained numpy support

[27Bslash6]

Summary

• Extend CacheKeyGenerator._normalize() with cross-language compatible type support
• Add custom key= parameter escape hatch for complex types
• Add comprehensive test coverage (67 new tests)

Supported Types

Type	Normalization	Cross-Language
Path	.as_posix()	✅
UUID	str(uuid)	✅
Decimal	str(decimal)	✅
Enum	.value (recursive)	✅
datetime	.isoformat() (UTC only)	✅
numpy.ndarray	1D, ≤100KB, i32/i64/f32/f64	✅

Array Constraints (per security review)

• 256-bit Blake2b hash - collision resistance at scale
• Little-endian byte order - cross-platform determinism
• 100KB per-array limit - memory safety
• 5MB aggregate limit - DoS prevention
• Version prefix __array_v1__ - protocol evolution

Rejected by Design

• set/frozenset - mixed-type sorting crashes
• pandas.DataFrame - Parquet serialization is non-deterministic

Escape Hatch

@cache(key=lambda arr: hashlib.blake2b(arr.tobytes()).hexdigest())
def process(arr: np.ndarray) -> float:
    return arr.mean()

Test plan

• make quick-check passes
• 53 key generator tests pass
• 14 custom key function tests pass
• CI passes

[codecov]

Codecov Report

❌ Patch coverage is 27.90698% with 62 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/cachekit/key_generator.py	32.35%	37 Missing and 9 partials ⚠️
src/cachekit/decorators/wrapper.py	5.88%	11 Missing and 5 partials ⚠️

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