Merge #17435: test: check custom ancestor limit in mempool_packages.py

<pre>Merge #17435: test: check custom ancestor limit in mempool_packages.py 49997813a4db388b2810e5e27ef771e8aa6a1f03 test: check custom ancestor limit in mempool_packages.py (Sebastian Falbesoner) Pull request description: The functional test `mempool_packages.py` starts one node with default ancestor/descendant limit settings and one with a custom, reduced ancestor limit (currently `-limitancestorcount=5`). The effect of the latter had not been tested yet though. This is approached in this PR by checking on the expected mempool contents of node1 after the node0 ancestor tests are done, via the following three conditions: - the # of txs in the node1 mempool is equal to the the limit - all txs in node1 mempool are a subset of txs in node0 mempool - the node1 mempool txs match the start of the constructed tx-chain Note that this still doesn't *fully* check the expected mempool of node1 (e.g. that it isn't influenced by `prioritisetransaction` RPC on node0), hence I add another TODO. In the future it would make sense to also set a custom descendant limit when the second TODO about checking node1's mempool is approached: https://github.com/bitcoin/bitcoin/blob/89e93135aedf984f7a98771f047e2beb6cdbdb8e/test/functional/mempool_packages.py#L228 ACKs for top commit: MarcoFalke: ACK 49997813a4db388b2810e5e27ef771e8aa6a1f03 &#128114; Tree-SHA512: d3a1d19fb49731238ad08ee7c02e2fa81a227e3b4ef3340d68598de42ddb62be9161134f6b8e08fa76b8c9faa02fecfa01111159642e20e9f358292a757b7608</pre>