Add SA executemany compiled cache support

[katajakasa]

Add compiled_cache support for SAConnection.executemany. Add tests for INSERT and UPDATE cases.

[codecov[bot]]

Codecov Report

Merging #376 into master will increase coverage by 0.03%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #376      +/-   ##
==========================================
+ Coverage   92.28%   92.32%   +0.03%     
==========================================
  Files           9        9              
  Lines        1180     1186       +6     
  Branches      172      174       +2     
==========================================
+ Hits         1089     1095       +6     
  Misses         64       64              
  Partials       27       27

Impacted Files	Coverage Δ
aiomysql/sa/connection.py	93.53% <100%> (+0.19%)	:arrow_up:

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[terricain]

Other than that list comprehension, it looks great :smile:

[katajakasa]

Okay, so I dropped the extra checks. Turns out those were not actually needed plus they were a perf hit when adding larger amounts of rows. Also added a testcase for DELETE :)

[terricain]

This good to go now?

[katajakasa]

@terrycain Yes, this is good to go.