Set a global fork graph in program cache

[pgarg66]

Problem

LoadedPrograms::prune() is passed an instance of fork graph. Same information can be used in few other methods in the cache. It'll be ideal if the fork_graph can be set globally for the cache.

Summary of Changes

Set fork_graph at startup and use it in prune.

Fixes #

[codecov]

Codecov Report

Merging #33776 (8a44175) into master (7aa0fae) will decrease coverage by 0.1%.
Report is 15 commits behind head on master.
The diff coverage is 92.1%.

@@            Coverage Diff            @@
##           master   #33776     +/-   ##
=========================================
- Coverage    81.8%    81.8%   -0.1%     
=========================================
  Files         806      806             
  Lines      217937   218009     +72     
=========================================
+ Hits       178322   178378     +56     
- Misses      39615    39631     +16     

[Lichtso]

Think this can be removed again.

[pgarg66]

Removing it causes the following error

error[E0277]: `BankForks` doesn't implement `std::fmt::Debug`
   --> runtime/src/bank.rs:823:5
    |
661 | #[derive(AbiExample, Debug)]
    |                      ----- in this derive macro expansion
...
823 |     pub loaded_programs_cache: Arc<RwLock<LoadedPrograms<BankForks>>>,
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `BankForks` cannot be formatted using `{:?}`

[Lichtso]

Then manually: impl Debug for LoadedPrograms {}. Should do that anyway because it contains a lot of things that are unhelpful to display.

[pgarg66]

Yes, agree. Would be better as a separate PR.

[Lichtso]

This should to be a Weak reference.

[andreisilviudragnea]

Funny that I came across the same problem now: anza-xyz#1893

[mergify]

Backports to the stable branch are to be avoided unless absolutely necessary for fixing bugs, security issues, and perf regressions. Changes intended for backport should be structured such that a minimum effective diff can be committed separately from any refactoring, plumbing, cleanup, etc that are not strictly necessary to achieve the goal. Any of the latter should go only into master and ride the normal stabilization schedule.