Internal structs for ThreadAware AccountRead/WriteLocks

[apfitzge]

Problem

Running an experiment w/ unlocking threads which requires using a DashMap inside the thread aware locks struct.
The interface for DashMap is slightly different, and we cannot do in-place tuple destructuring like is currently done; The code ended up having .0, or .1 in several places which feels very brittle and less readable.

Summary of Changes

Create simple structs to hold Account-specific read and write locks w/ named fields.
This makes changes (described above) cleaner if we end up doing that.

Fixes #

[apfitzge]

For reference, w/ this PR changing to using DashMaps becomes significantly simpler: 73bdfa2

Where the changes are limited to imports, types, and removing mutability.

Not sure the experiment will pan out, but think the change in this PR is good regardless.

[codecov]

Codecov Report

Merging #31431 (3b71f4f) into master (4b0e16d) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##           master   #31431   +/-   ##
=======================================
  Coverage    81.5%    81.5%           
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  Files         734      734           
  Lines      207159   207171   +12     
=======================================
+ Hits       168959   168988   +29     
+ Misses      38200    38183   -17     

[tao-stones]

lgtm