Add withContext to improve error reporting

[johnynek]

close #43

This follows the design sketched in the issue above. The goals are:

1. not break compatibility
2. not add a performance tax on those not using the feature
3. enable users to add strings to track where they are in a parser.

cc @kubukoz @mpilquist

[codecov-io]

Codecov Report

Merging #194 (3b906eb) into main (f9bd3fa) will increase coverage by 0.54%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #194      +/-   ##
==========================================
+ Coverage   95.63%   96.18%   +0.54%     
==========================================
  Files           7        7              
  Lines         939      969      +30     
  Branches       79       96      +17     
==========================================
+ Hits          898      932      +34     
+ Misses         41       37       -4     

Impacted Files	Coverage Δ
core/shared/src/main/scala/cats/parse/Parser.scala	95.87% <100.00%> (+0.65%)	⬆️

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[kubukoz]

Looks good to me! Although some test with an example and not as much logic as in the existing prop tests would be nice.

[kubukoz]

Can we make this tailrec? It'd probably require a reverse at the end but maybe it's worth pursuing?

[johnynek]

Seems to me if your errors are so nested you blow the stack here you will have other issues. I don't think it is worth a cost to retain the ability of having 50k deep nested contexts.

What do you think?

[kubukoz]

Fair. Let's leave it ;)

[johnynek]

This is published as part of 0.3.3