Refactor lowering code to use Arenas/cleanup

[edg-l]

Refactors the lowering code to use arenas, and also use it to cleanup the lowering code as now i know more or less the patterns.

[github-actions]

Benchmarking factorial

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1298 lines in your changes missing coverage. Please review.

Project coverage is 44.00%. Comparing base (c253cdb) to head (730a688).

Files with missing lines	Patch %	Lines
src/ir/lowering2/expressions.rs	0.00%	333 Missing ⚠️
src/ir/lowering2/lower.rs	0.00%	309 Missing ⚠️
src/ir/lowering2/ir.rs	0.00%	218 Missing ⚠️
src/ir/lowering2/mod.rs	0.00%	176 Missing ⚠️
src/ir/lowering2/types.rs	0.00%	141 Missing ⚠️
src/ir/lowering2/functions.rs	0.00%	47 Missing ⚠️
src/ir/lowering2/constants.rs	0.00%	38 Missing ⚠️
src/ir/lowering2/statements.rs	0.00%	26 Missing ⚠️
src/ast/types.rs	0.00%	10 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##           struct_generics     #175       +/-   ##
====================================================
- Coverage            58.49%   44.00%   -14.50%     
====================================================
  Files                   21       29        +8     
  Lines                 4014     5293     +1279     
====================================================
- Hits                  2348     2329       -19     
- Misses                1666     2964     +1298     

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