fix: drop collections at end of each sample

[diberry]

Each vector search sample now drops its collection after the search completes, ensuring no leftover collections accumulate between runs.

Changes (13 files):

• TypeScript (ivf.ts, hnsw.ts, diskann.ts): Drop collection in finally block before closing connection
• Python (ivf.py, hnsw.py, diskann.py): Drop collection in finally block before closing connection
• Go (ivf.go, hnsw.go, diskann.go): Drop collection before final success message
• Java (IVF.java, HNSW.java, DiskAnn.java): Drop collection after vector search completes
• .NET (VectorSearchService.cs): Drop collection after printing search results

All changes are minimal — just adding the drop call at the appropriate cleanup point in each sample.