fix: output to stdout instead of stderr

[ep0chzer0]

Summary

Changes logging output from stderr to stdout for better Unix CLI compatibility.

Problem

Slither outputs detector and printer results to stderr instead of stdout, which goes against Unix CLI tool expectations and makes piping/grepping awkward:

# Before: doesn't work as expected
slither . > output.txt        # output.txt is empty, output goes to console
slither . | grep "reentrancy" # nothing found, need `2>&1` workaround

Solution

Changed logging.StreamHandler() to logging.StreamHandler(sys.stdout) in:

• slither/__main__.py
• slither/tools/erc_conformance/__main__.py
• slither/tools/kspec_coverage/__main__.py
• slither/tools/properties/__main__.py

After this change

slither . > output.txt        # captures slither output correctly
slither . | grep "reentrancy" # works as expected

Notes

• Per @montyly's comment on why does slither output to stderr instead of stdout? #753: "This and stderr are for legacy reasons - but we can change it now"
• The exit code behavior (0/non-zero) is already correct and unchanged

Fixes #753

🤖 Generated with Claude Code

[ep0chzer0]

Hi maintainers, could you please approve the CI workflow runs for this PR? As a first-time contributor, the workflows require maintainer approval. Thank you!

[elopez]

We need to ensure this doesn't break other tools' expectations, e.g. slither . --print echidna --json - should only have valid JSON on stdout and not any other messages.

[ep0chzer0]

Thanks for the feedback @elopez! I've updated the PR to address this concern.

Changes:

• When --json - or --sarif - is used, logs now go to stderr to preserve valid JSON/SARIF on stdout
• Normal usage (no JSON to stdout) still benefits from stdout logging for better Unix CLI compatibility

I also reverted the changes to the tool subcommands since they set up logging at module level before args are parsed.

The behavior is now:

• slither . > output.txt - captures logs (normal usage)
• slither . --json - > output.json - only valid JSON in file, logs to stderr