feat: add token frequencies

[cheb0]

Description

Adds token frequency which can be used to optimize query performance

---

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

[codecov-commenter]

Codecov Report

❌ Patch coverage is 84.09091% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.58%. Comparing base (25381c2) to head (2aad996).

Files with missing lines	Patch %	Lines
frac/sealed/token/block_loader.go	83.90%	7 Missing and 7 partials ⚠️
cmd/index_analyzer/main.go	0.00%	4 Missing ⚠️
indexwriter/blocks.go	80.00%	1 Missing and 1 partial ⚠️
cmd/seq-db/seq-db.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #438      +/-   ##
==========================================
+ Coverage   70.51%   70.58%   +0.06%     
==========================================
  Files         232      232              
  Lines       18268    18376     +108     
==========================================
+ Hits        12881    12970      +89     
- Misses       4426     4438      +12     
- Partials      961      968       +7     

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[github-actions]

🔴 Performance Degradation

Some benchmarks have degraded compared to the previous run.
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Name	Previous	Current	Ratio	Verdict
Sealing_NoSort-4	25381c	6afc04
	5314.00 allocs/op	6000.00 allocs/op	1.13	🔴
Sealing_WithSort-4	25381c	6afc04
	5370.00 allocs/op	6074.00 allocs/op	1.13	🔴

[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
Sealing_NoSort-4	25381c	1d308e
	5314.00 allocs/op	5977.00 allocs/op	1.12	🔴
Sealing_WithSort-4	25381c	1d308e
	5370.00 allocs/op	6044.00 allocs/op	1.13	🔴

[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=1000000-4	25381c	8e734e
	4659647.00 ns/op	5193054.00 ns/op	1.11	🔴
Not/size=10000-4	25381c	8e734e
	4.51 ns/op	5.02 ns/op	1.11	🔴
Not/size=1000000-4	25381c	8e734e
	4.66 ns/op	5.22 ns/op	1.12	🔴
ParseESTime/es_stdlib-4	25381c	8e734e
	182.30 ns/op	204.10 ns/op	1.12	🔴
ParseESTime/handwritten-4	25381c	8e734e
	39.96 ns/op	44.60 ns/op	1.12	🔴
ParseESTime/rfc3339-4	25381c	8e734e
	51.37 ns/op	57.38 ns/op	1.12	🔴