rpc/store: align list-limit metadata and document query limits

[namedfarouk]

Summary

• align SyncNullifiers list-limit validation in RPC and store with the parameter semantics (nullifier_prefix)
• expose the same SyncNullifiers parameter key via GetLimits
• extend GetLimits test coverage to assert SyncNullifiers and SyncNotes limits
• expand internal RPC docs with a concrete query-limits table and rationale

Why

Issue #1080 asks to revisit/document list parameter limits.

This keeps limit handling consistent across:

• runtime validation
• GetLimits response metadata
• tests
• internal docs

Validation

• cargo test -p miden-node-rpc get_limits_endpoint
• cargo check -p miden-node-store -p miden-node-rpc

Closes #1080

[namedfarouk]

Superseded by #1986 (same changes on a clean branch name + issue assignment request flow).