Fix persisting attributes changed in-place

[andrykonchin]

The v3.9.0 release introduced a bug when in-place changes of attributes aren't detected and saved.

The issue affected in-place changes of string fields, modifying fields of compound types array/map/raw, serialized and custom types.

Example of in-place changing:

user = User.find('id')

user.name.upcase!
user.save

Example of modifying a field of compound type:

user = User.find('id')

user.settings[:namespace] = 'us-west'
user.save

Fixes #749, #814, #738, #666

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.56%. Comparing base (75a55b2) to head (37572d7).
Report is 51 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #829      +/-   ##
==========================================
+ Coverage   91.44%   91.56%   +0.12%     
==========================================
  Files          75       75              
  Lines        3645     3700      +55     
==========================================
+ Hits         3333     3388      +55     
  Misses        312      312              

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[github-actions]

Package	Line Rate	Health
dynamoid	92%	➖
Summary	92% (3384 / 3696)	➖

Minimum allowed line rate is 90%