feat: catchup to agave, until 2025-08-07 + bank-related modifications

[ksn6]

NOTE: in addition to catching up, we make the following modifications:

(1) To accommodate anza-xyz/agave@b82d3bb:

• Eliminate root_bank_cache.rs and use SharableBank instead
• Gotta correct this spelling error in Agave later.

(2) To accommodate anza-xyz/agave@dc0f51a:

• Eliminate LeaderBankNotifier in block_creation_loop.rs
• Write a "bank cleared notifier" condvar that notifies the loop once the bank has been cleared (or a timeout happens).

These modifications are important to make now rather than later; otherwise, we cannot cherry-pick all commits that get us on track to Agave. It's dangerous to selectively cherry-pick commits; we don't want to risk cherry-picking a later commit that indirectly depends on something we skipped, or else weird bugs may occur.

[wen-coding]

NOTE: in addition to catching up, we make the following modifications:

(1) To accommodate anza-xyz/agave@b82d3bb:

• Eliminate root_bank_cache.rs and use SharableBank instead
• Gotta correct this spelling error in Agave later.

(2) To accommodate anza-xyz/agave@dc0f51a:

• Eliminate LeaderBankNotifier in block_creation_loop.rs
• Write a "bank cleared notifier" condvar that notifies the loop once the bank has been cleared (or a timeout happens).

These modifications are important to make now rather than later; otherwise, we cannot cherry-pick all commits that get us on track to Agave. It's dangerous to selectively cherry-pick commits; we don't want to risk cherry-picking a later commit that indirectly depends on something we skipped, or else weird bugs may occur.

Is it possible to split into two PRs:

• Everything up to anza-xyz/agave@dc0f51a, including 1), because that should be lower risk
• anza-xyz/agave@dc0f51a and the corresponding fix?
  Because I feel (2) seems to be higher risk

[ksn6]

NOTE: in addition to catching up, we make the following modifications:
(1) To accommodate anza-xyz/agave@b82d3bb:

• Eliminate root_bank_cache.rs and use SharableBank instead
• Gotta correct this spelling error in Agave later.

(2) To accommodate anza-xyz/agave@dc0f51a:

• Eliminate LeaderBankNotifier in block_creation_loop.rs
• Write a "bank cleared notifier" condvar that notifies the loop once the bank has been cleared (or a timeout happens).

These modifications are important to make now rather than later; otherwise, we cannot cherry-pick all commits that get us on track to Agave. It's dangerous to selectively cherry-pick commits; we don't want to risk cherry-picking a later commit that indirectly depends on something we skipped, or else weird bugs may occur.

Is it possible to split into two PRs:

• Everything up to anza-xyz/agave@dc0f51a, including 1), because that should be lower risk
• anza-xyz/agave@dc0f51a and the corresponding fix?
  Because I feel (2) seems to be higher risk

Discussed offline - I think we're good to merge everything into this PR given that we're replacing the condvar stuff with a simple sleep.