Fix chunked response size overflow

[MrAlias]

Motivation

• The manual chunked HTTP decoder parsed the chunk size as a signed int64 and added it to a slice index without checking for overflow, allowing an attacker-controlled large chunk size to cause a runtime panic and crash the agent.

Description

• Parse the chunk-size line with strconv.ParseUint and remove the signed-negative check to avoid incorrect casting.
• Compute available := len(data) - chunkStart and treat any chunkSize greater than available as a truncated chunk before converting to int and slicing.
• Add a regression test in TestDechunkBody that asserts an oversized advertised chunk ("7fffffffffffffff\r\nA") is treated as truncated and returns the available bytes.

Testing

• go test ./pkg/ebpf/common -run 'TestDechunkBody|TestHttpSafeParseResponseChunked'

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.07%. Comparing base (914ffa4) to head (b75acc4).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/ebpf/common/http_transform.go	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2520      +/-   ##
==========================================
- Coverage   69.24%   69.07%   -0.18%     
==========================================
  Files         345      345              
  Lines       46747    46796      +49     
==========================================
- Hits        32372    32326      -46     
- Misses      12330    12435     +105     
+ Partials     2045     2035      -10     

Flag	Coverage Δ
integration-test	50.30% <60.00%> (-0.62%)	⬇️
integration-test-arm	27.10% <0.00%> (-1.21%)	⬇️
integration-test-vm-5.15-lts	?
integration-test-vm-6.18-lts	?
k8s-integration-test	36.03% <0.00%> (+0.33%)	⬆️
oats-test	35.45% <60.00%> (+0.09%)	⬆️
unittests	63.36% <80.00%> (+0.04%)	⬆️

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[grcevski]

LGTM!