Add cache TTL and max hits to zsh completion caching

[nat-n]

Description of changes

This PR enhances the zsh completion caching mechanism with two important features to prevent serving stale data:

1. In-Memory Cache TTL (Time-To-Live)

• Adds timestamp tracking for in-memory cached task descriptions and arguments
• Implements a 1-hour TTL (matching the disk cache policy) for in-memory cache entries
• Prevents indefinitely serving stale data from in-memory cache within long-lived shell sessions
• Tracks timestamps using zsh's $SECONDS variable in _poe_mem_tasks_time and _poe_mem_args_time associative arrays

2. Max Cache Hits Threshold

• Introduces a hit counter mechanism that forces a fresh fetch after N cache hits (default: 10)
• Applies to both task descriptions and task arguments caching
• Resets counter to 0 after a forced refresh, allowing cache to be used again
• Prevents serving stale cached data indefinitely even when disk cache TTL hasn't expired
• Tracks hits in _poe_cache_hits_tasks and _poe_cache_hits_args associative arrays

3. Cache Policy Pattern Fix

• Fixes cache policy zstyle pattern to use wildcard matching (":completion:*:${0#_}*:*")
• Ensures cache policy is discoverable after _arguments -C modifies curcontext
• Previously, the literal context pattern wouldn't match when _arguments -C appended state suffixes (e.g., poe → poe-args)

4. Code Refactoring

• Extracts task fetching logic into a new _poe_fetch_tasks() helper function
• Consolidates hybrid caching logic (disk → in-memory → fresh fetch) in one place
• Reduces code duplication between task state and help_task state handlers
• Improves maintainability and testability

Testing

• Adds comprehensive test suite covering:
  • Cache policy pattern matching across different curcontext states
  • In-memory cache TTL expiration behavior
  • Max cache hits threshold enforcement
  • Cache hit counter reset after forced refresh
  • Behavior for both task descriptions and task arguments
  • Help task state caching

All new features are covered by tests in test_zsh_completion_harness.py.

Pre-merge Checklist

• New features are covered by new feature tests
• Bug fixes are accompanied by tests
• Code changes follow existing patterns and conventions
• This PR targets the development branch

https://claude.ai/code/session_017koSbdzwCoQ2evAwnRkpbN