fix(tarpit): honor connection notes when there is no transaction - #3641

Changes proposed in this pull request:

• tarpit returned early when connection.transaction was null, before reading connection.notes.tarpit. The note is documented in docs/plugins/tarpit.md, but the connect, helo and ehlo hooks run before a transaction exists, so the delay was skipped there.
• It now uses connection.notes.tarpit, falling back to connection.transaction?.notes?.tarpit.
• Adds a test for the no-transaction case and a CHANGELOG entry.

I did not run the tests locally. CI on my fork:

• Test only (81f5818): fails on ubuntu 22/24/26, macOS and Windows. The log shows ✖ delays when connection.notes.tarpit is set and there is no transaction, AssertionError [ERR_ASSERTION]: should have waited ~100ms. Run: https://github.com/ChandraChaan/Haraka/actions/runs/41612305065
• With the fix (c44de10, this PR): lint, prettier, coverage and all OS jobs pass. Run: https://github.com/ChandraChaan/Haraka/actions/runs/41612308807

Checklist:

• docs updated (no change needed, the docs already describe this behavior)
• tests updated
• CHANGELOG updated