Update state: apply header, verify, store

[lukaszrzasik]

Closes #<ISSUE_NUMBER>

This PR:

This PR does not:

Key places to review:

[imabdulbasit]

I think we should just move these checks

// Check internal consistency.
    let parent_header = parent_leaf.block_header();
    ensure!(
        state.chain_config.commit() == parent_header.chain_config().commit(),
        "internal error! in-memory chain config {:?} does not match parent header {:?}",
        state.chain_config,
        parent_header.chain_config(),
    );
    ensure!(
        state.block_merkle_tree.commitment() == parent_header.block_merkle_tree_root(),
        "internal error! in-memory block tree {} does not match parent header {}",
        state.block_merkle_tree.commitment(),
        parent_header.block_merkle_tree_root()
    );
    ensure!(
        state.fee_merkle_tree.commitment() == parent_header.fee_merkle_tree_root(),
        "internal error! in-memory fee tree {} does not match parent header {}",
        state.fee_merkle_tree.commitment(),
        parent_header.fee_merkle_tree_root()
    );

from before to after apply_header(), and we can change them for proposals instead of parent WDYT?

[lukaszrzasik]

I wanted to split the code into separate logical parts: apply, verify, store. I can just move the code if that's what you prefer.

[github-actions]

Backport failed for release-20251106, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin release-20251106
git worktree add -d .worktree/backport-3756-to-release-20251106 origin/release-20251106
cd .worktree/backport-3756-to-release-20251106
git switch --create backport-3756-to-release-20251106
git cherry-pick -x e574cda8d540aa44842f821d3618ba556b31ad10