meter, config: meter public and private response traffic independently (#993)

[ti-chi-bot]

This is an automated cherry-pick of #993

What problem does this PR solve?

Issue Number: close #990

Problem Summary:
The costs for public endpoint and private endpoint traffic are different, so meter them independently.

What is changed and how it works:

• Add a config proxy.public-endpoints to pass in the public NLB IP or CIDR.
• Move the parsing CIDR and matching CIDR functions into netutil.
• Update outBound_bytes to private_outBound_bytes and public_outBound_tytes of the metering system.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Notable changes

• Has configuration change
• Has HTTP API interfaces change
• Has tiproxyctl change
• Other user behavior changes

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: djshow832

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Details

Needs approval from an approver in each of these files:

• OWNERS [djshow832]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-11-27 05:36:05.835208441 +0000 UTC m=+767529.484402898: ☑️ agreed by djshow832.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 12 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-nextgen-20251023@1f96aff). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pkg/util/netutil/netutil.go	71.87%	6 Missing and 3 partials ⚠️
pkg/proxy/proxy.go	40.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@                     Coverage Diff                     @@
##             release-nextgen-20251023     #994   +/-   ##
===========================================================
  Coverage                            ?   67.63%           
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  Files                               ?      137           
  Lines                               ?    13505           
  Branches                            ?        0           
===========================================================
  Hits                                ?     9134           
  Misses                              ?     3740           
  Partials                            ?      631           

Flag	Coverage Δ
unit	67.63% <80.00%> (?)

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