Use one Session for the whole download

[aclerc]

Example failing tests: https://github.com/resgroup/wind-up/actions/runs/28163240915/job/83408733375?pr=100
One Session for the whole download so its connection pool (and every socket) is closed deterministically on exit.

[Copilot]

Pull request overview

This PR addresses leaked SSL sockets during Zenodo downloads by routing all HTTP requests through a single requests.Session that is closed deterministically at the end of the download.

Changes:

• Wrap download_zenodo_data() in a single requests.Session() context and pass that session into _download_one_file().
• Add an offline regression test that asserts all requests go through the shared session and that the session is closed exactly once.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
benchmarking/synthetic/sources/hill_of_towie.py	Use one shared requests.Session for metadata + file downloads; _download_one_file now uses the provided session.
tests/benchmarking/synthetic/sources/test_hill_of_towie.py	Adds a regression test ensuring all requests route via one Session and that it’s closed once.

Comments suppressed due to low confidence (1)

benchmarking/synthetic/sources/hill_of_towie.py:193

• If result.raise_for_status() raises (e.g., 4xx/5xx), the streamed Response is never closed because the with (result, ...) block is not entered. That can still leak a socket/connection for error responses. Close the response before re-raising so the outer except requests.RequestException can handle it without leaving the connection open.

            result = session.get(
                _file_url,
                stream=True,
                timeout=(_CONNECT_TIMEOUT_S, _READ_TIMEOUT_S),
                headers=headers,
            )
            result.raise_for_status()

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