Add brutal EdgeCases and Stress test suites

EdgeCases Tests (35+ tests):
- Subnormal number handling (smallest values, normal/subnormal boundaries)
- Sign bit edge cases (±0, sign preservation, infinity signs)
- ULP (Unit in Last Place) edge cases (adjacent representable numbers)
- Extreme values (maximum finite, one ULP below infinity)
- NaN bit patterns (quiet/signaling NaN, different payloads)
- Endianness edge cases with special values
- Bit pattern validation (all zeros, sign bit only, max exponent)

Stress Tests (22+ tests):
- Volume tests (10,000 random conversions for Double/Float)
- Rapid conversion tests (1,000 back-and-forth round-trips)
- Concurrent access consistency (async serialization/deserialization)
- Magnitude range sweeps (1e-308 to 1e308 for Double)
- Bit pattern exhaustion (all 256 byte values in each position)
- Deterministic behavior validation
- Memory efficiency tests (no leaks with 10K iterations)

All 137 tests in 44 suites passing (0 swiftlint violations).

These tests catch bugs that commonly break other IEEE 754 implementations:
- Incorrect subnormal number handling
- Sign bit corruption on special values
- Endianness bugs with edge cases
- Non-deterministic serialization
- Memory leaks under load

Author: coenttb