Add comprehensive bug hunt test suite for critical issues

[dave-hillier]

Summary

This PR adds a comprehensive test suite that documents and validates fixes for 7 critical bugs discovered across the Nemcache codebase. These tests serve as regression tests to ensure bugs do not reoccur and provide clear documentation of the issues and their expected behavior.

Bugs Addressed

1. ConsistentHashRing Duplicate Nodes Bug

• Issue: GetNodes() returns duplicate physical nodes because it walks virtual-node positions without deduplicating
• Impact: Reduced replication factor and potential deadlocks in Orleans grains
• Test: ConsistentHashRingDuplicatesBugTest validates that distinct physical nodes are always returned

2. BitcaskStore Tombstone Loading Bug

• Issue: LoadIndex() does not handle tombstones (deleted entries marked with empty values)
• Impact: Deleted keys reappear after store reload
• Test: BitcaskTombstoneLoadIndexBugTest ensures deleted keys remain deleted across restarts

3. HybridLogStore MemoryStream Corruption Bug

• Issue: TryGet() corrupts the MemoryStream write position by not restoring it after reading
• Impact: Subsequent Put() operations overwrite existing data
• Test: HybridLogTryGetCorruptionBugTest validates data integrity after read operations

4. Decrement Underflow Bug

• Issue: MemCache.Mutate() performs unsigned subtraction without underflow protection
• Impact: Decrementing below zero wraps to huge numbers instead of clamping to 0
• Test: DecrementUnderflowBugTest ensures decrement operations clamp at zero per memcached protocol

5. MutateRequestBuilder NoReply Bug

• Issue: ToAsciiRequest() appends boolean string "True" instead of protocol keyword "noreply"
• Impact: Invalid protocol messages sent to server
• Test: MutateRequestBuilderNoReplyBugTest validates correct protocol keyword emission

6. TouchHandler Response Bug

• Issue: Returns "OK\r\n" instead of "TOUCHED\r\n" per memcached protocol
• Impact: Protocol non-compliance, client confusion
• Test: TouchResponseBugTest validates correct response keyword

7. VersionHandler Response Bug

• Issue: Returns "Nemcache {version}\r\n" instead of "VERSION {version}\r\n"
• Impact: Protocol non-compliance
• Test: VersionResponseBugTest validates correct response format

Implementation Details

• All tests are organized in Nemcache.Tests/BugHuntTests/ directory
• Tests use NUnit framework consistent with existing test suite
• Each test includes detailed XML documentation explaining the bug, its impact, and the fix location
• Tests cover both happy path and edge cases to ensure comprehensive validation
• Temporary file/directory cleanup is properly handled in persistence tests

https://claude.ai/code/session_01J98sY8MUjVDKUP47MY1Fvn