Module level const support

[cburgdorf]

What was wrong?

We currently do not yet support constant values (see #192)

How was it fixed?

This PR adds support for const on the module level but only for base types. I also have some WIP code to also support complex types but since base types can simply be inlined (no point in wasting gas to read them from the code) we can handle support for these constants entirely at the lowering stage which is what this PR does.

To-Do

• OPTIONAL: Update Spec if applicable
• Add entry to the release notes (may forgo for trivial changes)

[codecov-commenter]

Codecov Report

Merging #536 (49ed5e4) into master (466d4b5) will decrease coverage by 0.38%.
The diff coverage is 3.84%.

@@            Coverage Diff             @@
##           master     #536      +/-   ##
==========================================
- Coverage   87.67%   87.29%   -0.39%     
==========================================
  Files          87       87              
  Lines        5672     5697      +25     
==========================================
  Hits         4973     4973              
- Misses        699      724      +25     

Impacted Files	Coverage Δ
crates/parser/src/ast.rs	62.90% <0.00%> (-1.04%)	⬇️
crates/parser/src/grammar/module.rs	66.34% <4.00%> (-19.91%)	⬇️

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[sbillig]

LGTM