feat: add KeyRecipe and KeyRecipeCache

This commit adds the key recipe system for translating requests to
sortable string format (ssformat) keys for routing.

Key components:
- KeyRecipe: Translates requests to ssformat keys using server-provided recipes
- KeyRecipeCache: Caches recipes by request fingerprint for efficient reuse
- PreparedRead: Helper class for preparing read requests with routing info
- RecipeGoldenTest: Golden tests for recipe encoding validation
- RecipeTestCases: Test case definitions for recipe tests

This is part of the experimental location-aware routing for improved latency.

Author: rahul2393