Improve memory reservations in ModuleBuilder

[Robbepop]

This should optimize ModuleBuilder::finish and generally the building process of Wasm modules.

Locally I can see some minor 2-5% performance wins especially for the lazy translation test cases where the impact is especially visible.

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 80.83%. Comparing base (26ea8ad) to head (3861ae3).
Report is 1 commits behind head on master.

Files	Patch %	Lines
crates/wasmi/src/module/builder.rs	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1032      +/-   ##
==========================================
- Coverage   80.83%   80.83%   -0.01%     
==========================================
  Files         269      269              
  Lines       24803    24817      +14     
==========================================
+ Hits        20049    20060      +11     
- Misses       4754     4757       +3     

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