EVM Node: use intermediate RPC node in tezt for multichain

What

This MR sets the spawn_rpc feature whenever executing a multichain test.

It then fixes all tests that break, in particular when the sequencer node is restarted and the related rpc needs to be ready before serving requests again.

Why

Many tests rely on the sequencer to answer common RPC requests. However, in the multichain scenario the set of RPCs implemented by the sequencer is restricted, as implemented in !16991 (merged).

How

Creating a fresh port and passing it to the register_test_for_kernels when the enable_mutlichain feature is enabled.

Manually testing the MR

dune exec etherlink/tezt/tests/main.exe -- alpha sequencer multichain_enabled /dal /threshold_encryption /mainnet /ghostnet /flaky

The only test currently not passing on the command above is also broken on master, namely:

Alpha: Sequencer use remote server to get preimages with retries (sequencer, latest, without dal, multichain)