chore: add structured logging with secret redaction

[mogita]

Ticket

https://linear.app/stream/issue/CHA-2957/logging

Summary

Adds structured logging via the existing logger: kwarg (stdlib Logger): client.initialized, http.request.sent, http.response.received, http.request.failed. Mandatory redaction of secret query params and known-secret body keys. Opt-in log_bodies with a one-shot WARN.

Behavior change

The prior $stdout fallback for the pool-config line is removed; with no logger injected the client produces no output.

Tests

make test green (294); spec/logging_spec.rb covers events, redaction, the no-logger case, and the transport-message scrub.

[mogita]

Titled chore: (not feat:) intentionally: this repo's Release workflow derives the version bump from the PR-title type and skips releasing when the type is not feat/fix, so merging this will not auto-publish. The change is a feature; when you want to publish, run the Release workflow manually (workflow_dispatch, version bump = minor).