Add logging

[xbt-a4224j]

Proposal, feedback welcome!

• Add slf4j logging on a io.github.premocloud.typesafe logger. DEBUG: one line per request with status, elapsed and request id, plus a line per retry and per connection failure (transport.py:73-94). TRACE: the wire in both directions — method, url, headers, body (_log_wire, client.ts:344-396). A tier below the references, since Spring Boot's default root level is INFO and theirs filter it out.

• Nothing at INFO or above: neither reference has a WARN or ERROR call site, and failures already throw (TypeSafeApiException), which carries more than a log line would.

• No TYPESAFE_LOG_LEVEL as in the reference impls: slf4j has no library-side level setting, and per the FAQ libraries "should let the end-user configure the logging environment". README should specify logging.level.io.github.premocloud.typesafe={DEBUG|TRACE}.

• One redaction point, as with SensitiveHeadersFilter and redactHeaders, so no call site can leak. "***" as in python, set from SECRET_HEADERS plus the _is_secret "token"/"secret" check, since Builder.header lets a caller add one this SDK never anticipated.

Sample monitoring output:

#1
DEBUG io.github.premocloud.typesafe - req-1 <- 200 in 754ms (request req_01a0bc4f...)

#2
TRACE io.github.premocloud.typesafe - req-1 -> POST https://api.typesafe.ai/v1/systemone headers={Accept=application/json, Authorization=***, ...} body={"state":...}
DEBUG io.github.premocloud.typesafe - req-1 <- 200 in 649ms (request req_01a0bc4f...)
TRACE io.github.premocloud.typesafe - req-1 <- 200 headers={:status=200, x-typesafe-request-id=req_01a0bc4f..., ...} body={"model":"jev-1.13.0",...}