Keep request futures local to sherlock

[jameswjr]

Summary

This keeps request futures local to sherlock() instead of storing them inside the caller-provided site_data dictionaries.

Rationale

Although Sherlock is primarily used as a CLI, sherlock() is an importable function and is already called directly in the test suite. A wrapper, integration, or downstream test can reasonably pass in
a site_data object and expect it to remain site metadata rather than become temporary request-state storage.

Currently, the function iterates through site_data like this:

for social_network, net_info in site_data.items():

Inside that loop, net_info is the per-site dictionary from site_data. The current implementation stores runtime request state there:

net_info["request_future"] = future

and reads it back later.

This is harmless in the normal one-shot CLI path, because the mutated site_data is usually discarded. But it can surprise callers that reuse, inspect, compare, serialize, or share the same site_data
object.

This PR preserves the existing two-pass flow, but stores futures in a local dictionary keyed by social-network name instead.

Behavior

This should preserve user-visible behavior. It changes only where temporary request futures are stored during the call.

The invalid-username path is still handled: when no future is created, the site already has a status, and the second pass continues before reading from the local futures dictionary.

Test

Added a focused no-network regression test that fakes the futures session and asserts that sherlock() does not mutate the supplied site_data.

Local validation

python3 -m py_compile sherlock_project/sherlock.py tests/test_ux.py

I prepared this outside a fully installed Sherlock development environment, so I was not able to run the focused pytest command locally. The intended focused test command is:

python -m pytest -q tests/test_ux.py::test_sherlock_does_not_mutate_input_site_data

[ppfeister]

Disregard the docker build failure, that's unrelated to your PR.
Will take a look shortly. Might be a good change.