perf: implement batch processing in iterateEvalTree

[cheb0]

Description

Continuation of #390

• iterateEvalTree works with batches of lids, requests batches of mids and rids
• fixes stopwatch measurements for get_mid step
• array based hist map is decoupled into it's own struct

I did some measurements for both patches (this combined with #390) vs main (used bitpack encoding in both branches). For small ordinary searches there is no benefit. For dense analytic queries there is a decent improvement.

For our k6 benchmark seq-db-hist.js: 2.3 sec => 650 ms
For seq-db-aggs.js: 6.1 sec => 4.7 sec
Hist over _all_ (warm query) (3 prod fractions): ~37 ms => ~15 ms

Part of #329

---

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

[cheb0]

@seqbenchbot up main search-keyword-exact-match-warm

[seqbenchbot]

Nice, @cheb0 <(-^,^-)=b!

Your request was successfully served.
Identificator for your ongoing benchmark - e8eefca9.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 78.76712% with 31 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.58%. Comparing base (da8604a) to head (74748b8).

Files with missing lines	Patch %	Lines
frac/processor/search.go	71.26%	22 Missing and 3 partials ⚠️
frac/sealed/seqids/provider.go	70.00%	2 Missing and 1 partial ⚠️
frac/sealed_index.go	72.72%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@                Coverage Diff                 @@
##           329-batching-1     #406      +/-   ##
==================================================
- Coverage           71.54%   70.58%   -0.97%     
==================================================
  Files                 220      221       +1     
  Lines               16568    20423    +3855     
==================================================
+ Hits                11854    14415    +2561     
- Misses               3840     5128    +1288     
- Partials              874      880       +6     

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[cheb0]

@seqbenchbot down e8eefca9

[seqbenchbot]

Nice, @cheb0 <(-^,^-)=b!

The benchmark with identificator e8eefca9 was finished.
I've prepared a summary for you. Click on Show summary button to see it:

Show summary

Query	Type	mean (ms)			stddev (ms)			p(50) (ms)			p(95) (ms)			p(99) (ms)			iterations
		base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff	base	comp	diff
bulk	warm	65.92	67.00	+1.65%	25.11	26.77	+6.60%	58.00	60.00	+3.45%	118.00	124.00	+5.08%	157.50	165.00	+4.76%	2450.00	2450.00	0.00%
service:payment-backend-eu AND k8s_namespace:prod	warm	130.57	129.30	-0.97%	115.82	112.04	-3.26%	114.00	115.00	+0.88%	324.00	319.00	-1.54%	669.50	642.50	-4.03%	8339.00	8363.00	+0.29%

Have a great time!