Enclose check_next_block Call with Debug Assertions for Validators

[kpandl]

Motivation

The check_next_block function incurs significant processing time, which contributes to increased block times. For validators participating in consensus, the checks performed by this function are redundant, as they are already handled elsewhere in the codebase. This PR encloses the check_next_block call within debug assertions (#[cfg(debug_assertions)]) to optimize performance and reduce block times in production environments.

Test Plan

Ran it locally. Todo: Further stress tests (load, syncing).

To verify that all checks remain adequately covered, you can find useful notes in this diff:

check_next_block.patch

[raychu86]

What are the heavy parts of the check_next_block call?

The Transaction verification results should be cached already; are there other parts of the verification process that are costly? Maybe the db lookups?

[kpandl]

Based on a flamegraph analysis, the most time-consuming operation within the check_next_block function is compute_finalize_root.

While there is potential to further optimize by caching, it seems worth investigating how we can skip check_next_block entirely to optimally reduce the block time, since other parts of the function may become bottlenecks with larger committee sizes.

Please note that we should run certain stress tests (load, syncing) before merging the PR.