feat(saf): add Micrometer metrics instrumentation

[ar-agt]

This PR implements Chhil's Prompt Request to add Micrometer instrumentation to the jPOS-EE SAF module, following a red-green-refactor flow and mirroring the existing QRestMetrics pattern.

Because this is our first Prompt Request, a quick note on the idea is here:
https://jpos.org/blog/2026/02/prompt-requests

What's included:

• Added package-private SAFMetrics with null-safe no-op behavior when no MeterRegistry is configured
• Added SAF meters:
  • jpos.saf.queue.size
  • jpos.saf.send.duration
  • jpos.saf.send.success
  • jpos.saf.send.retried
  • jpos.saf.send.expired
  • jpos.saf.send.discarded
• Wired metrics into SAF.initService() and SAF.send(Entry)
• Added micrometer.core to modules/saf module-info
• Added SAF test dependencies and a new SAF test suite

Behavior covered by tests:

• no-op behavior when metrics are not configured
• queue depth gauge registration
• send duration recording
• success / retry / expired / discarded counters
• SAF send-path instrumentation for success, retry, timeout, ISOException, expiration, and max retransmissions

Verification:

• ./gradlew :modules:saf:test
• git diff --check

[ar-agt]

Thanks, @chhil.

I implemented your Prompt Request and opened this PR. I followed a TDD flow and kept the SAF metrics pattern aligned with QRestMetrics, including null-safe no-op behavior when no registry is configured.

Since this is the first Prompt Request we're receiving, here's the short write-up on the idea as well:
https://jpos.org/blog/2026/02/prompt-requests

[chhil]

The prompt missed adding update the module_saf.adoc with metrics changes.

[chhil]

Should 2 events get logged if its max retransmission and expired?
i.e. preserves both when both conditions apply