Eliminate dependency on serde's "derive" feature

[dtolnay]

This allows serde, and other crates downstream of it like serde_json, to compile in parallel with serde_derive. Without this PR, in any dependency graph that pulls in serde_with, first serde_derive would need to compile, then serde would need to compile, then serde_json would need to compile.

sharkdp/bat#2815 has a diagram of the impact of this change.

[dtolnay]

CI failures look unrelated to this change. See #695.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2b17850) 65.41% compared to head (5e6a115) 65.41%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #694   +/-   ##
=======================================
  Coverage   65.41%   65.41%           
=======================================
  Files          38       38           
  Lines        2322     2322           
=======================================
  Hits         1519     1519           
  Misses        803      803           

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[jonasbb]

Thank you for the PRs. This looks ok, but I think it re-introduces the risk of mismatching serde dependency versions. Bumping the serde dependency to v1.0.186 should mitigate this. I can bump the dependency and release a new patch version.

[dtolnay]

Thank you, that would be great. Yes, serde 1.0.186+ contains serde-rs/serde#2588 which eliminates the version mismatch possibility.

[jonasbb]

v3.6.1 is published now