refactor(pxe): batch RPC calls for note and event validation

[nchamo]

Summary

• Refactors note and event validation in the PXE to prefetch tx effects once per unique tx hash and pass them as a map to batch methods, eliminating redundant RPC calls when multiple notes/events share a transaction
• Consolidates nullifier lookups into a chunked batch helper, replacing per-note RPC calls with a single batched call
• Adds a uniqueBy utility to the foundation collection library for deduplicating arrays by a key function

[Thunkar]

Lovely! Would feel better if @mverzilli took a look too though