Evaluate whether UnsolicitedMessageHandler::Matches can test IsInUse() without codesize impact

[bzbarsky-apple]

Problem

After https://github.com/project-chip/connectedhomeip/pull/5606, UnsolicitedMessageHandler::Matches needs to be called only when IsInUse() is known to be true. We could add an IsInUse() test inside Matches(), but need to check codesize impact. Which is hard right now because that code is not actually used in anything we measure codesize for.

Proposed Solution

Wait for https://github.com/project-chip/connectedhomeip/pull/5095 or equivalent to land, then do the measuring.

[bzbarsky-apple]

Or #5627

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[stale[bot]]

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[bzbarsky-apple]

Measured this on esp32 just now, and it's a slight (4 bytes) codesize hit. Probably not worth it.