feat: add DocsFilter

[forshev]

Description

Added DocsFilter struct. Not in use yet

---

• I have read and followed all requirements in CONTRIBUTING.md;
• I used LLM/AI assistance to make this pull request;

If you have used LLM/AI assistance please provide model name and full prompt:

Model: {{model-name}}
Prompt: {{prompt}}

[codecov-commenter]

Codecov Report

❌ Patch coverage is 32.35908% with 324 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.32%. Comparing base (ad03474) to head (0506ad3).

Files with missing lines	Patch %	Lines
docsfilter/docs_filter.go	0.00%	206 Missing ⚠️
docsfilter/encoding.go	78.80%	17 Missing and 15 partials ⚠️
util/fs.go	38.77%	17 Missing and 13 partials ⚠️
docsfilter/filter.go	0.00%	16 Missing ⚠️
asyncsearcher/async_searcher.go	22.22%	2 Missing and 5 partials ⚠️
frac/active.go	25.00%	6 Missing ⚠️
frac/active_index.go	0.00%	6 Missing ⚠️
frac/remote.go	0.00%	6 Missing ⚠️
frac/active_lids_map.go	66.66%	5 Missing ⚠️
frac/sealed.go	0.00%	4 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #371      +/-   ##
==========================================
- Coverage   71.42%   70.32%   -1.10%     
==========================================
  Files         205      209       +4     
  Lines       14910    15335     +425     
==========================================
+ Hits        10650    10785     +135     
- Misses       3484     3759     +275     
- Partials      776      791      +15     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

🔴 Performance Degradation

Some benchmarks have degraded compared to the previous run.
Click on Show table button to see full list of degraded benchmarks.

Show table

Name	Previous	Current	Ratio	Verdict
AggDeep/size=10000-4	ad0347	e19aad
	47818.00 ns/op	54318.00 ns/op	1.14	🔴
AggWide/size=1000-4	ad0347	e19aad
	4780.00 ns/op	5615.00 ns/op	1.17	🔴
And/size=1000-4	ad0347	e19aad
	4.49 ns/op	5.14 ns/op	1.14	🔴

[github-actions]

🔴 Performance Degradation

Some benchmarks have degraded compared to the previous run.
Click on Show table button to see full list of degraded benchmarks.

Show table

Name	Previous	Current	Ratio	Verdict
AggDeep/size=1000-4	ad0347	6ba4f4
	4737.00 ns/op	5455.00 ns/op	1.15	🔴
AggWide/size=1000-4	ad0347	6ba4f4
	4780.00 ns/op	5329.00 ns/op	1.11	🔴
FindSequence_Random/medium-4	ad0347	6ba4f4
	12292.95 MB/s	9431.80 MB/s	0.77	🔴
	86.31 ns/op	108.60 ns/op	1.26	🔴