GroMEt For Loop PR

[titomeister]

Implements changes to GroMEt generation to support for loop generation for Python.

• Makes use of the 'init' field in GroMEt FNs that have a loop.
• Introduces functions to interact with iterators ('next', 'init') in CAST.
• Fixes some other minor bugs that prevented GroMEts for simple expressions and functions to be generated.
• Fixed the metadata indexing issue.
• Improves how the primitive generation is handled, though more work is needed to make it fully complete. We now keep track of how many inputs/outputs each primitive uses, which is needed for generating GroMEts of primitive functions.

[codecov[bot]]

Codecov Report

Merging #320 (d5771cd) into master (6c3f09c) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #320   +/-   ##
=======================================
  Coverage   36.25%   36.25%           
=======================================
  Files         112      112           
  Lines       22485    22485           
=======================================
  Hits         8153     8153           
  Misses      14332    14332           

Impacted Files	Coverage Δ
...lysis/CAST2GrFN/ann_cast/grfn_var_creation_pass.py	87.26% <ø> (ø)
...ates/program_analysis/PyAST2CAST/py_ast_to_cast.py	11.39% <ø> (ø)

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