fix(searching_tool): normalize guard, runtime param overrides, 1D query safety

[agentksimha]

Four targeted fixes for silent bugs and missing runtime flexibility.

Problem

• metric='ip' without L2-normalization returns wrong similarity rankings with no indication anything is wrong
• nprobe (IVFPQ) and efSearch (HNSW) were fixed at build time with no way to tune them per-query at search time
• Passing a 1D query vector caused inconsistent output shapes across the three return paths in search()

Changes

• Add normalize(X) utility for L2-normalization before indexing
• Add _warn_if_unnormalized() called in all three build functions — samples up to 64 rows, zero overhead at scale
• Add nprobe= and efsearch= optional overrides to search(); original values saved and restored in a finally block so the bundle is never left in a dirty state
• Add 1D shape guard at the top of search(); was_1d flag ensures output shape always matches input

No breaking changes — all new params are optional with None defaults.