refactor: move test utility functions to separate crate

[Wodann]

No description provided.

[codecov]

Codecov Report

Merging #253 into master will decrease coverage by 0.00%.
The diff coverage is 83.50%.

@@            Coverage Diff             @@
##           master     #253      +/-   ##
==========================================
- Coverage   79.11%   79.10%   -0.01%     
==========================================
  Files         201      201              
  Lines       12767    12807      +40     
==========================================
+ Hits        10100    10131      +31     
- Misses       2667     2676       +9     

Impacted Files	Coverage Δ
crates/mun_test/src/driver.rs	69.81% <69.81%> (ø)
crates/mun_runtime/tests/hot_reloading.rs	100.00% <100.00%> (ø)
crates/mun_runtime/tests/marshalling.rs	98.19% <100.00%> (-0.81%)	⬇️
crates/mun_runtime/tests/memory.rs	100.00% <100.00%> (ø)
crates/mun_runtime/tests/runtime.rs	100.00% <100.00%> (ø)

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