Add query timing and debug logging to index execution paths

[tylerhutcherson]

Summary

Add query timing and debug logging around index execution paths for better observability.

Level: Intermediate

Current State

• Logging exists in some RedisVL components, but query execution paths are lightly instrumented.
• Performance triage often requires ad hoc local instrumentation.

Proposed Change

• Add debug logs for sync/async query execution in redisvl/index/index.py:
  • query category/type
  • elapsed time (ms)
  • result count
• Add optional slow-query warning threshold.

Definition of Done

• Query timing appears in debug logs for sync and async paths.
• No functional behavior changes to query results.
• Overhead is negligible when debug logging is disabled.

Out of Scope

• Full tracing backend integration (OpenTelemetry, etc.).

[nabilasiregar]

I'll pick this up