fix: restore method/params in WS send-caching dummy request (#3823)

[saheersk]

Title:
fix: restore method/params in WS send-caching dummy request (#3823)

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Body:

When async_handle_send_caching detects a cache hit it returns a dummy
RPCRequest (id=-1) to skip the network send. Previously the dummy used
method="" and params=[], so async_handle_recv_caching could not compute
the correct cache key and fell through to _get_response_for_request_id(-1),
causing a TimeExhausted error on every cached WS request.

Fix: preserve the original method and params in the dummy request so the
recv-caching decorator can look up and return the cached response.

Also move import threading in cache_request_information to module level.

Add three tests covering the persistent-connection (WebSocket) caching
path: end-to-end socket_request caching, dummy request preservation,
and recv-caching round-trip.

What was wrong?

Related to Issue #3823
Closes #3823

For PersistentConnectionProvider (WebSocket/AsyncIPC), cacheable RPC
requests (e.g. eth_chainId) were never served from cache — every call
hit the network.

Root cause: async_handle_send_caching returns a dummy RPCRequest
(id=-1) when it detects a cache hit, to prevent the request from being
sent over the wire. The dummy used method="" and params=[], so when
async_handle_recv_caching received it, is_cacheable_request returned
False (empty method is not on the allowlist). The decorator then called
_get_response_for_request_id(-1), which polled until TimeExhausted.

A secondary contributing bug: the cache key in cache_request_information
used a different format from the one used by the caching decorators
(missing the thread-ID prefix), so the early-exit guard that prevents
duplicate request-info entries never fired.

How was it fixed?

• async_handle_send_caching now preserves the original method and params
  in the dummy request ({"id": -1, "method": method, "params": params}),
  so async_handle_recv_caching can compute the correct cache key and
  return the cached response without touching the network.
• import threading moved from inside cache_request_information to module
  level in request_processor.py.
• Three new tests added for the persistent-connection caching path:
  end-to-end socket_request cache hit, dummy request field preservation,
  and full send->recv cached round-trip.

Todo:

• Clean up commit history
• Add or update documentation related to these changes
• Add entry to the release notes (https://github.com/ethereum/web3.py/blob/main/newsfragments/README.md)

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