Support block bundling/elastic scaling for parachains

[bkchr]

Right now Smoldot is assuming that parachains are just progressing by one block per relay chain block. However, with block bundling (putting multiple blocks into one PoV) or just using elastic scaling (having the parachain running on multiple cores at once) parachains will progress more than one block per relay chain block. While smoldot is able to keep up with these chains, transactions are not getting processed correctly, because it doesn't download the block bodies of the blocks being "jumped over".
The parachain sync algorithm should be similar to the one from the relay chain, aka follow the block announcements. Only finality should be based on what is determined by looking into the relay chain.

[eskimor]

Related: Plan is to go to 500ms blocks - what impact will this have on smoldot (performance)?

[bkchr]

It will need to track more blocks/headers. Also the window of unfinalized blocks will be bigger.