feat: add QPR mem size limit

[cheb0]

Description

Introduces QPR heap memory limit in order to prevent some OOMs on proxy.

Part of #373

---

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

[github-actions]

🔴 Performance Degradation

Some benchmarks have degraded compared to the previous run.
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Name	Previous	Current	Ratio	Verdict
AggWide/size=10000-4	ad0347	5eae03
	47541.00 ns/op	54446.00 ns/op	1.15	🔴

[codecov-commenter]

Codecov Report

❌ Patch coverage is 55.35714% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.48%. Comparing base (03387c3) to head (c1151cd).

Files with missing lines	Patch %	Lines
seq/qpr.go	62.79%	10 Missing and 6 partials ⚠️
proxy/search/ingestor.go	0.00%	3 Missing and 1 partial ⚠️
fracmanager/searcher.go	50.00%	1 Missing and 1 partial ⚠️
storeapi/grpc_v1.go	33.33%	1 Missing and 1 partial ⚠️
cmd/seq-db/seq-db.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #374      +/-   ##
==========================================
+ Coverage   71.40%   71.48%   +0.08%     
==========================================
  Files         206      206              
  Lines       15057    15113      +56     
==========================================
+ Hits        10751    10804      +53     
+ Misses       3523     3514       -9     
- Partials      783      795      +12     

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[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
FindSequence_Random/small-4	03387c	876482
	6427.67 MB/s	4642.84 MB/s	0.72	🔴
	40.85 ns/op	55.14 ns/op	1.35	🔴