replace snowflaked to avoid conflicts

[gallone2000]

Replace snowflaked crate with custom implementation

Overview

This PR removes the external snowflaked dependency and replaces it with a custom, lock-free snowflake ID generator implementation. The new implementation maintains full behavioral compatibility with snowflaked 1.0.3 while providing equivalent or improved performance characteristics.

Key Changes

• Removed dependency: Moved snowflaked from production to dev-dependencies (used only for testing/oracle validation)
• Custom generator: Implemented a deterministic, thread-safe snowflake generator using atomic CAS operations with Relaxed ordering
• Bit layout: Maintains the exact same 42/10/12 bit partitioning (timestamp/instance/sequence) as the original crate
• Behavior parity: Clock rollback handling, sequence overflow with millisecond wait, and timestamp extraction match the oracle exactly

Test Coverage

I implemented comprehensive test suites to ensure robustness and guard against future regressions:

Deterministic Tests

• Single and multi-threaded uniqueness and monotonicity
• System time extraction and Unix epoch alignment
• Millisecond boundary transitions
• u63 boundary handling
• JSON serialization roundtrips
• Model-based scripted state transitions with controlled clock

Oracle-Based Tests

• Bit-for-bit packing equivalence with snowflaked::Snowflake::from_parts
• Failure mode validation: both implementations panic identically on clock rollback

Property-Based Tests

• Generated with proptest to explore large input spaces automatically
• Roundtrip pack/unpack preservation of components
• Boundary-biased strategies covering edge cases (0, max, near-max values)
• Monotonicity and uniqueness under varying sample sizes
• u63 boundary behavior for all valid input combinations

Includes CI-friendly seed control via PROPTEST_SEED env var for deterministic property test execution.

Performance

Benchmark suite included for regression detection.

Rationale

The custom implementation:

1. Eliminates an external dependency while maintaining full compatibility
2. Provides transparent behavior through extensive oracle testing
3. Reduces operational risk via property-based testing of edge cases
4. Scales equally or better under concurrent load