[WIP] Add microbenchmarks and improve efficiency of core functions

[tonybaloney]

Introduces a pytest extension "pytest-benchmark" and runs microbenchmarks of key functions within the worker process.

This PR will also include some optimizations.

Fork of #1039 - so that should be merged first

[tonybaloney]

Comparison of first patch 699bbbc refactoring the build_binding_protos() function with 0-9 bindings shows a consistent 10-15% reduction in execution time.

[tonybaloney]

Profiles for loader.index_function_app() are showing the function is relatively slow because:

• the standard library inspect module is notoriously slow
• The clean nones wrapper is quite inefficient
• The JSON dumps happening on the function metadata is done eagerly (and not cached)?

[JoseIvanHernandez]

Commit