rewrite some checksum related code

[TingDaoK]

Issue #, if available:

• Get into this rabbit hole from removing body_user_callback_after_checksum to support write into file directly

Description of changes:

• No functionality change, beside I modified the request response header directly instead of making a copy.
• Remove the *_after_checksum callbacks, just invoke the right function from the right place
• we don't need to make a copy of headers before we send it to the user, we are not using the response headers anymore afterwards
• reuse some code instead of copy/paste

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.17204% with 11 lines in your changes missing coverage. Please review.

Project coverage is 89.44%. Comparing base (94e3342) to head (6698fc9).

Files	Patch %	Lines
source/s3_meta_request.c	89.79%	5 Missing ⚠️
source/s3_util.c	88.46%	3 Missing ⚠️
source/s3_auto_ranged_get.c	66.66%	2 Missing ⚠️
source/s3_default_meta_request.c	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #443      +/-   ##
==========================================
- Coverage   89.62%   89.44%   -0.19%     
==========================================
  Files          20       20              
  Lines        6092     6080      -12     
==========================================
- Hits         5460     5438      -22     
- Misses        632      642      +10     

Files	Coverage Δ
source/s3_auto_ranged_put.c	92.78% <100.00%> (-0.02%)	⬇️
source/s3_default_meta_request.c	95.23% <88.88%> (-0.52%)	⬇️
source/s3_auto_ranged_get.c	97.23% <66.66%> (-0.55%)	⬇️
source/s3_util.c	97.16% <88.46%> (-0.78%)	⬇️
source/s3_meta_request.c	92.77% <89.79%> (-0.69%)	⬇️