[Enhancement]: Remove deepcopy in patch_model

[SingleZombie]

Motivation

When patch_model, we have to deepcopy a model, which increases the memory overhead.

Modification

Remove deepcopy and add comments.

[codecov]

Codecov Report

Merging #61 (315c8c0) into master (d1528e5) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #61      +/-   ##
==========================================
- Coverage   67.60%   67.59%   -0.01%     
==========================================
  Files         173      173              
  Lines        5713     5712       -1     
  Branches      908      908              
==========================================
- Hits         3862     3861       -1     
  Misses       1569     1569              
  Partials      282      282              

Flag	Coverage Δ
unittests	67.59% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
mmdeploy/core/rewriters/rewriter_manager.py	100.00% <ø> (ø)
mmdeploy/core/rewriters/module_rewriter.py	95.12% <100.00%> (-0.12%)	⬇️

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[RunningLeon]

LGTM