Fix decorator AST visitor dispatch

[wunianze666-netizen]

Summary

• fix the ast.NodeVisitor callback registration so FunctionDef nodes are actually visited
• route decorator-argument diagnostics through structured debug logging instead of stdout
• add a regression test that exercises a real decorator call with an AST argument

Why

NodeVisitor dispatches function definitions to visit_FunctionDef, but the helper registered visit_function_def. As a result, get_decorators() returned an empty mapping and the intended visitor logic never ran. Correcting the dispatch exposes the existing unconditional print(), so the diagnostic is now kept behind the project logger.

Validation

• py -m uv run --package soda-tests --group dev pytest soda-tests/tests/unit/test_soda_tracer.py -q (1 passed)
• py -m uv run black --check soda-tests/tests/unit/test_soda_tracer.py
• git diff --check

CI note

The GitHub Actions matrix currently stops before test execution in the upstream Get external secrets step because fork runs do not receive the AWS region/Secrets Manager configuration (expected region to be configured for aws.auth#sigv4). The fork-safe pre-commit, lockfile, CLA, Aikido, and SonarCloud checks pass; the targeted unit test above passes locally.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[wunianze666-netizen]

CI follow-up: all 13 failing Python 3.14 matrix jobs stop in the Get external secrets step before tests run. The AWS Secrets Manager action receives empty fork credentials/region and reports expected region to be configured for aws.auth#sigv4. The pre-commit/lockfile checks and Sonar quality gate pass, so this does not appear to be a source-code failure that can be fixed in the PR branch. Could a maintainer rerun the matrix in a trusted context or apply the repository's fork-safe workflow path?