Cleanup - load_and_get_programs_from_cache()

[Lichtso]

Problem

Currently the global cache is locked for every single program that is replenished. But one write lock would suffice.
Also, assign_program() should only be used for program management instructions.

Summary of Changes

• Only lock the global cache once all missing programs have been loaded.
• Factors out call of self.rc.accounts.filter_executable_program_accounts() into caller.
• Replaces assign_program() by replenish().
• Replaces LoadedProgramEntry by a boolean.

[pgarg66]

Looks great

[codecov]

Codecov Report

Merging #30959 (957a9cf) into master (2646fb7) will increase coverage by 0.0%.
The diff coverage is 55.9%.

@@           Coverage Diff           @@
##           master   #30959   +/-   ##
=======================================
  Coverage    81.5%    81.5%           
=======================================
  Files         728      728           
  Lines      205467   205430   -37     
=======================================
- Hits       167532   167507   -25     
+ Misses      37935    37923   -12