[Docs] update FAQ with logprobs MQ limits and deprecation

[sunlei1024]

Motivation

Improve the FAQ documentation by adding details about message size limits when logprobs is enabled and clarifying that the current System V message-queue–based communication mechanism will be deprecated in future versions.

Modifications

• Updated FAQ section describing inference stalls caused by System V Message Queue limits.
• Added detailed message-size calculation examples for MTP and non-MTP modes.
• Added guidance on adjusting kernel.msgmax and kernel.msgmnb.
• Added a deprecation notice indicating that this communication method will be removed in future releases.

Usage or Command

N/A — documentation-only update.

Accuracy Tests

N/A — no changes to model behavior or inference logic.

Checklist

• Add at least a tag in the PR title. Suggested: [Docs]
• Format updated documentation.
• No unit tests needed (documentation-only).
• No accuracy results needed.
• Not a cherry-pick PR.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (develop@5cd17fd). Learn more about missing BASE report.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #5368   +/-   ##
==========================================
  Coverage           ?   59.71%           
==========================================
  Files              ?      325           
  Lines              ?    40286           
  Branches           ?     6100           
==========================================
  Hits               ?    24057           
  Misses             ?    14337           
  Partials           ?     1892           

Flag	Coverage Δ
GPU	59.71% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[paddle-bot]

Thanks for your contribution!