Replace direct wat usage with Wasmi's new Module::new Wat support

[Robbepop]

Follow-up for #1328.

tl;dr: Cleans-up the Wasmi workspace and resolves some tech-debt.

A test-only wat2wasm function has been implemented several times in the Wasmi codebase, especially in tests which is an indicator that this functionality was crucially missing from Wasmi's module parsing.

[codecov]

Codecov Report

Attention: Patch coverage is 99.43074% with 3 lines in your changes missing coverage. Please review.

Project coverage is 81.68%. Comparing base (c889d43) to head (e87e1b2).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/cli/src/context.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1327      +/-   ##
==========================================
+ Coverage   81.62%   81.68%   +0.06%     
==========================================
  Files         305      307       +2     
  Lines       25287    25261      -26     
==========================================
- Hits        20641    20635       -6     
+ Misses       4646     4626      -20     

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