Fix stale-template timeout assignment during block template rotation

[MoneroOcean]

Motivation

• The pool must penalize miners who continue mining a previous block more than 4 seconds after it is replaced by stamping the outgoing active template with a timeoutTime so submit-path decay/rejection logic can run.
• A prior change accidentally assigned timeoutTime to pastBlockTemplates[coin].get(0) (an already-past entry) instead of the template being retired, allowing the just-replaced template to be enqueued without timeoutTime and bypass stale-share handling.

Description

• Assign timeoutTime on the outgoing template itself via previousTemplate.timeoutTime = Date.now() + 4 * 1000 before enqueueing it into pastBlockTemplates.
• Preserve existing circular buffer initialization by creating pastBlockTemplates[coin] when missing and then calling pastBlockTemplates[coin].enq(previousTemplate).
• This change is implemented in lib/pool/templates.js and restores the intended 4-second grace window for the just-staled template so submit logic that checks blockTemplate.timeoutTime will trigger correctly.

Testing

• Ran the project test runner with npm -s test, which could not complete in this environment due to a missing dependency (protocol-buffers), so the full automated test-suite did not run successfully.

---

Codex Task