Close FTP file handles when a transfer raises

[itej13]

FTPHook.retrieve_file and FTPHook.store_file opened a local file and then ran the FTP transfer before calling close(). If the transfer raised — a routine occurrence for network I/O — the handle was never closed and leaked for the lifetime of the process.

Wrapping the transfer in try/finally guarantees the handle we opened is always closed, while still leaving a caller-supplied file-like buffer open (the method's existing contract). Adds regression tests for both methods that fail without the fix.

closes: #69077

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Was generative AI tooling used to co-author this PR?

• Yes — Claude Code (Opus 4.8)

Generated-by: Claude Code (Opus 4.8) following the guidelines

[boring-cyborg]

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[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.