feat: include more context in errors

[ajatprabha]

Current errors do not provide much info into where to look for malformed values. This change aims to provide more context around errors.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0020145) 98.97% compared to head (919eca4) 98.85%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #31      +/-   ##
==========================================
- Coverage   98.97%   98.85%   -0.12%     
==========================================
  Files          35       36       +1     
  Lines         781      789       +8     
==========================================
+ Hits          773      780       +7     
- Misses          8        9       +1     

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[sonnes]

Is it possible to support errors.Is? Something like

if errors.Is(err, xload.ErrRequired):
   ...

[ajatprabha]

Is it possible to support errors.Is? Something like

if errors.Is(err, xload.ErrRequired):
   ...

errors.Is would not work as it cannot work with struct types but only initialized variables, errors.As will work instead, syntax would look like:

var reqErr xload.ErrRequired
if errors.As(err, &reqErr) {
	...
}