Various changes related to the fork detection script

[ImplOfAnImpl]

A bunch of miscellaneous changes:

1. Some changes initially included in Fork detection script #1968:
   • New node option "--allow-checkpoints-mismatch".
   • last_tip_block_time is now included in the peer info returned by the corresponding node RPC call.
   • In p2p, peer id is now logged automatically via a tracing span, so its explicit logging is no longer needed and was removed.
     Also, tracing spans are now propagated when subsystem calls are made. This way when p2p calls the chainstate and something happens, we'll know the peer id that caused it.
2. The "New peer accepted" log line now also includes the user agent and its version.
3. Chainstate's preliminary_block_check and preliminary_headers_check now check if the block already exists. This fixes a bug where if a peer was too slow, we could receive an already existing block from it when the block height was already below the reorg limit, which would lead to it being punished for nothing.
4. Trait HasSubObjWithSameId. Useful to be able to produce WithId<&SignedBlockHeader> from &WithId<Block> without recalculating the id.
5. The ability to force the chainstate to print full block ids in the log (via the tracing target "chainstate_verbose_block_ids").
6. New node option "--custom-checkpoints-csv-file" allowing to specify custom checkpolints (useful when investigating a fork)
7. Some minor cleanup here and there.