converts remaining unstructured errors to use fferr

[epps]

Description

This PR converts remaining unstructured errors to use fferr package.

Type of change

Select type(s) of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have fixed any merge conflicts

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 55.81%. Comparing base (6395449) to head (f44bc12).

Files	Patch %	Lines
provider/clickhouse.go	0.00%	3 Missing ⚠️
provider/k8s.go	0.00%	2 Missing ⚠️
filestore/filepath.go	0.00%	1 Missing ⚠️
provider/filestore.go	0.00%	1 Missing ⚠️
serving/serving.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1374   +/-   ##
=======================================
  Coverage   55.80%   55.81%           
=======================================
  Files         189      189           
  Lines       24721    24723    +2     
  Branches      833      833           
=======================================
+ Hits        13796    13799    +3     
- Misses       9392     9393    +1     
+ Partials     1533     1531    -2     

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