Revert named-blob client-disconnect guard (#3279, #3281)

[nicolaslopezbravo]

Summary

Reverts #3279 (Cancel named-blob metadata commit when client has disconnected) and its dependent follow-up #3281 (Classify client-disconnect during named-blob PUT as 400, not 500).

#3279 added a best-effort restRequest.isOpen() guard in AmbryIdConverterFactory.NamedBlobIdConverter#convertId that skips the named-blob metadata commit and throws when the client has already disconnected. #3281 then changed that throw from RestServiceException(RequestChannelClosed) to a client-termination IOException so it classified as 400 rather than 500.

The guard can race with other exception paths on the same request, so the error a disconnected named-blob PUT reports is not deterministic. The correct fix for the underlying PUT retry race landed separately, so the guard is redundant.

Why both PRs

#3281 only refines the guard block #3279 introduced, so it has no remaining subject once #3279 is gone. Reverting #3279 alone would leave import java.io.IOException and the IOException on convertId's throws clause with nothing able to throw it.

Changes

Revert of #3279:

• AmbryIdConverterFactory: remove the isOpen() guard.
• FrontendMetrics: remove idConverterClientAbortedCount.
• NettyMessageProcessor.channelInactive(): remove the request.close() call added before onRequestAborted(...).
• Remove ambryIdConverterNamedBlobPutClientDisconnectTest and the NettyMessageProcessorTest cases added alongside it.

Revert of #3281:

• AmbryIdConverterFactory: drop the java.io.IOException import and the IOException on convertId's throws clause.

This restores a duplicate import com.github.ambry.utils.Utils; (lines 36 and 45). #3281's description attributed that duplicate to #3279, but it is present in 367375cd6^, so it predates both PRs; it is left in place to keep the revert faithful.

Verification

git diff 367375cd6^ HEAD over all five touched files is empty, so the branch is master with both PRs removed and nothing else.

Testing Done

• ./gradlew :ambry-frontend:compileTestJava :ambry-rest:compileTestJava — BUILD SUCCESSFUL
• ./gradlew :ambry-frontend:test --tests '*AmbryIdConverterFactoryTest' — 2 tests, 2 passed, 0 failed
• ./gradlew :ambry-rest:test --tests '*NettyMessageProcessorTest' — 9 tests, 9 passed, 0 failed

Built with JDK 11; the repo's sourceCompatibility = 1.8 does not compile under JDK 25.

Risk / ops impact

Low — a revert to previously-shipped behavior. No interface, wire, or schema changes. The idConverterClientAbortedCount metric is removed, and classification of client disconnects during named-blob PUT returns to its pre-#3279 behavior. Backout is a revert of this PR.

AI usage

Revert prepared and verified with GitHub Copilot CLI.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.19%. Comparing base (52ba813) to head (9f05834).
⚠️ Report is 408 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (52ba813) and HEAD (9f05834). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (52ba813)	HEAD (9f05834)
	3	2

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3284       +/-   ##
=============================================
- Coverage     64.24%   38.19%   -26.05%     
+ Complexity    10398     6479     -3919     
=============================================
  Files           840      938       +98     
  Lines         71755    80374     +8619     
  Branches       8611     9672     +1061     
=============================================
- Hits          46099    30700    -15399     
- Misses        23004    47197    +24193     
+ Partials       2652     2477      -175     

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