Ignore unchanged block-template refreshes and add test

[MoneroOcean]

Motivation

• Avoid rotating and re-broadcasting block templates when a refreshed template is identical to the active one to preserve template-specific state and reduce unnecessary work.

Description

• Add an early exit in setNewBlockTemplate to skip processing when the incoming template idHash matches the currently active template by using a previousTemplate reference.
• Replace repeated lookups of activeBlockTemplates[coin] with a previousTemplate local variable and enqueue that into pastBlockTemplates when rotating.
• Ensure the rotation logic still sets timeout values and isExtraCheck when necessary while using the previousTemplate variable.
• Add a unit test template manager ignores unchanged template refreshes to tests/pool/components/core.js that verifies unchanged templates are ignored and that template-specific state (extraNonce, extraNonce2, sharedNonceSubmissions) is preserved, while a truly new template resets that state.

Testing

• Ran the pool component unit tests including tests/pool/components/core.js via the project test suite, and the full test suite passed.
• The new test template manager ignores unchanged template refreshes passed and confirms preserved state for identical templates and reset on new templates.

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Codex Task