Refactor - mock_process_instruction()

[Lichtso]

Problem

#30702 introduced InstructionError::BuiltinProgramsMustConsumeComputeUnits but that can not be triggered in the tests because they never pass through InvokeContext::process_executable_chain().

Summary of Changes

• Uses InvokeContext::process_instruction() in mock_process_instruction().
• Uses InvokeContext::process_instruction() in tests of loader-v3.
• Only throw InstructionError::BuiltinProgramsMustConsumeComputeUnits if result.is_ok().

[tao-stones]

lgtm. Good call for adding result.is_ok(), thanks for updating tests

[tao-stones]

lgtm

[codecov]

Codecov Report

Merging #30893 (63f410c) into master (f226a34) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##           master   #30893   +/-   ##
=======================================
  Coverage    81.5%    81.5%           
=======================================
  Files         726      726           
  Lines      204914   204907    -7     
=======================================
+ Hits       167069   167092   +23     
+ Misses      37845    37815   -30