New type BiddableUnfinishedBlock to avoid checking TBV of blocks built

[ZanCorDX]

📝 Summary

In some replaced I replaced Box for BiddableUnfinishedBlock since BlockBuildingHelper is in the process of being built and might not have a good TBV.
By using BiddableUnfinishedBlock we model that the block is ready so it always has a true_block_value.

💡 Motivation and Context

Removes annoying tests for Some(true_block_value) where we know it should be always Some.

✅ I have completed the following steps:

• Run make lint
• Run make test
• Added tests (if applicable)

[github-actions]

Benchmark results for 3d462cf

Report: https://flashbots-rbuilder-ci-stats.s3.us-east-2.amazonaws.com/benchmark/3d462cf-883c888/report/index.html

Date (UTC)	2025-01-27T21:50:32+00:00
Commit	3d462cf8a67de719af01fa9998e5293f7fe4d407
Base SHA	883c888d216661dbf6a3c8665ff461a881dc9203

Significant changes

Benchmark	Mean	Status
gather_nodes_big_changes_account	-3.79%	Performance has improved.
root_hash_account_trie_no_cache	2.80%	Performance has degraded.
root_hash_storage_hash	2.82%	Performance has degraded.
ptr_trie_insert_only_3000	-7.14%	Performance has improved.