test: add logging to mock external signers #32928

1. 
   Sjors commented at 2:44 pm on July 9, 2025: member

   This will hopefully aid in debugging #32855.

   Because stdout and stderr are consumed by the node, the mock external signers can’t use them for logging.

   Instead have them print directly into test_framework.log, which can then be be retrieved via combine_logs.py.

   In preparation (and addtion) this PR starts with a few refactors:

   • move mock_signer_path helpers to util and reuse them between rpc_signer.py and wallet_signer.py
   • move the mocks from test/functional/mocks to test/functional: this is needed to avoid Python import hell in the next commits
   • have the mocks take advantage of the test_framework by extracting (and reusing) perform_pre_checks and mock_signer_psbt_path into util
   • extract the debug.log style Formatter into util so we can use it in the final commit
2. test: move mock signer path helpers to util b38e0578b7
3. DrahtBot added the label Tests on Jul 9, 2025
4. 
   DrahtBot commented at 2:44 pm on July 9, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32928.

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5. test: move mock external signers to parent dir d619f7d580
6. test: have signer mocks use test framework

   - reuse perform_pre_checks helper
   - add mock_psbt_path helper

   b65ea68aaf
7. test: move log formatter to util 58ac12331a
8. test: add logging to mock signers

   Because stdout and stderr are consumed by the node, we can't use them for logging. Instead have the mocks print directly into test_framework.log, which can then be be retrieved via combine_logs.py.

   3ff8e6643e
9. Sjors force-pushed on Jul 9, 2025
10. DrahtBot added the label CI failed on Jul 9, 2025
11. Sjors renamed this:
    test: add logging to mock signers
    test: add logging to mock external signers
    on Jul 9, 2025
12. DrahtBot removed the label CI failed on Jul 9, 2025

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