perf: reduce unnecessary copies, optimize Address comparison

[software-dov]

Includes various other performance optimizations and minor whitespace fixes.

Local testing cuts down Ads generation time to ~1m (and prevents OOM) and DialogflowCX from ~10 minutes to ~5 minutes.

[codecov]

Codecov Report

Merging #855 (5497db9) into master (7c185e8) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #855   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           26        27    +1     
  Lines         1608      1662   +54     
  Branches       328       339   +11     
=========================================
+ Hits          1608      1662   +54     

Impacted Files	Coverage Δ
gapic/utils/case.py	100.00% <ø> (ø)
gapic/utils/reserved_names.py	100.00% <ø> (ø)
gapic/generator/generator.py	100.00% <100.00%> (ø)
gapic/schema/api.py	100.00% <100.00%> (ø)
gapic/schema/metadata.py	100.00% <100.00%> (ø)
gapic/schema/wrappers.py	100.00% <100.00%> (ø)
gapic/utils/__init__.py	100.00% <100.00%> (ø)
gapic/utils/checks.py	100.00% <100.00%> (ø)
gapic/utils/options.py	100.00% <100.00%> (ø)

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[busunkim96]

Thank you!