Moves some accounts-db test-only code into a dev-context-only-utils feature

[brooksprumo]

Problem

To prepare for splitting the runtime crate, we'll need access to some private/test-only functions from accounts-db. To simplify that move, we can consolidate the test-only code within accounts-db into dev-context-only-utils feature blocks.

The AccountsDb accounts_hashes and accounts_delta_hashes fields were made public recently (#32671) to keep tests working. This PR only adds/moves code to return those two fields back to private. Future PRs can/will more move test-only accounts-db code into dcou blocks.

Summary of Changes

Add a dcou block for getting/setting the AccountsDb accounts hashes and accounts delta hashes, and update the callers.

Refer to #32169 for more information about dev-context-only-utils.

[brooksprumo]

@ryoqun Do you have any suggestions/thoughts on how to name dcou functions that exist to re-export private functions for tests?

Rust won't let me call the dcou-version set_accounts_delta_hash(), since there's already one. And the _for_tests() is not needed anymore, since it's now within a dcou block. But I can't think of a better name... Have you already pondered on this?

[ryoqun]

Have you already pondered on this?

yep. seems this is common use case for dcou, i encountered this problem already...

not the rename, but i hope you like the taste of #32822

[codecov]

Codecov Report

Merging #32748 (ab17ed5) into master (6eea38d) will decrease coverage by 0.1%.
Report is 6 commits behind head on master.
The diff coverage is 99.4%.

@@            Coverage Diff            @@
##           master   #32748     +/-   ##
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- Coverage    82.0%    82.0%   -0.1%     
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  Files         785      785             
  Lines      211192   211198      +6     
=========================================
- Hits       173200   173197      -3     
- Misses      37992    38001      +9