doc: document ZMQ notification behavior during reorgs and evictions #35480

Partially addresses #14278.

Expands doc/zmq.md to document notification behavior that is implemented in the source but not described anywhere in the docs:

rawtx / hashtx

• These topics re-publish transactions from disconnected blocks during a reorg
• They are suppressed for historical blocks connected to the assumeutxo background validation chainstate (consistent with rawblock/hashblock)

sequence (R removals)

• Clarify that R covers all mempool removal reasons except block inclusion: EXPIRY, SIZELIMIT, REORG, CONFLICT, REPLACED (RBF)
• Explicitly note that block-inclusion removals are not reported via R; subscribers should use rawblock/hashblock for those

Reorg ordering

• Document the sequence of events during a reorg: D (block disconnected) → R (evicted mempool txs) → C (block connected)

All behavior described here is derived directly from src/zmq/zmqnotificationinterface.cpp and src/txmempool.cpp.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35480.

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