Delete ESS checkfiles on the server too, not just locally

[alongd]

ARC uploads a Gaussian checkpoint as a wavefunction guess for each job and downloads it again afterwards. When a run terminates it deletes those files — but only on the local machine:

• delete_check_files(project_directory) walks <project_directory>/calcs;
• main.py calls it unconditionally at the end of a run, since keep_checks defaults to False;
• no code path anywhere deletes anything on the remote server.

So the documented policy — "they usually take up lots of space and are not needed after ARC terminates" — is half-implemented, and every checkpoint ARC has ever uploaded is still sitting in the remote project directory.

Measured impact. On a quota-managed cluster, 82.3% of a fully characterised species' 61.4 MiB footprint is exactly this class of file — the next largest class is 5.6× smaller — and 6.35 GiB had silently accumulated against a 300 GB quota. Nothing downstream reads the remote copy: thermochemistry is parsed from the primary output log, and the local copy is the one reused as a guess.

What this does. Adds SSHClient.delete_check_files and a delete_remote_check_files helper, and routes the existing teardown through a new ARC.clean_check_files. Design constraints kept deliberately tight:

• keep_checks=True keeps them everywhere, local and remote — the flag's meaning is unchanged;
• deletion is scoped to *.chk under the run's own remote project directory, using the same path construction job/adapter.py already uses, and no-ops if that directory does not exist;
• errors are logged and never raised. This runs after the science is done; an unreachable server at teardown is an inconvenience, not a reason to lose a run;
• servers named local are skipped; nothing about uploads, the wavefunction-guess mechanism, or keep_checks's default changes.

Tests cover all three: deleted with keep_checks=False (asserting only .chk, and only under this project's directory), kept with keep_checks=True, and a run completing normally when the server call raises. Verified as a regression test rather than a tautology — removing just the remote call while leaving the helper in place makes test_check_files_are_deleted_locally_and_remotely fail.

[alongd]

not alwyas running under 'runs', 'ARC_Projects'

[alongd]

what's the difference between this and arc.common.delete_check_files()?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.47%. Comparing base (d033cbb) to head (90d4838).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1000      +/-   ##
==========================================
+ Coverage   64.38%   64.47%   +0.08%     
==========================================
  Files         119      119              
  Lines       39601    39627      +26     
  Branches    10269    10275       +6     
==========================================
+ Hits        25499    25549      +50     
+ Misses      11121    11089      -32     
- Partials     2981     2989       +8     

Flag	Coverage Δ
functionaltests	64.47% <ø> (+0.08%)	⬆️
unittests	64.47% <ø> (+0.08%)	⬆️

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