v2.1: SIMD-0207: Raise block limit to 50M (backport of #4112)

[mergify]

Problem

• See SIMD-0207: Raise block limit to 50M #4026 (reverted)
• Fixed issue with above

Summary of Changes

• Bank initialization and on epoch boundaries will set limits from feature-set
  • override for u64::MAX in tests/benches

Fixes #

---

This is an automatic backport of pull request #4112 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 9e59baa has failed:

On branch mergify/bp/v2.1/pr-4112
Your branch is up to date with 'origin/v2.1'.

You are currently cherry-picking commit 9e59baae7.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   cost-model/src/cost_tracker.rs
	modified:   runtime/src/bank/tests.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   cost-model/src/block_cost_limits.rs
	both modified:   runtime/src/bank.rs
	both modified:   sdk/feature-set/src/lib.rs

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[bw-solana]

LGTM

[t-nelson]

this should be behind #[feature("dev-only-context-utils")] the only external place it's used is a test. though perhaps the test can simply be in this crate