Fix memory leak in fleet autoscaler webhook HTTP client

[markmandel]

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking

/kind bug

/kind cleanup
/kind documentation
/kind feature
/kind hotfix
/kind release

What this PR does / Why we need it:

• Change fasThread.state from fasState (value) to *fasState (pointer) so the cached http.Client persists across sync cycles instead of being recreated on every iteration.
• Drain HTTP response body before closing to allow http.Transport to reuse connections, preventing unbounded connection growth.

Which issue(s) this PR fixes:

https://agones.slack.com/archives/C9DGM5DS8/p1774882327112899

Special notes for your reviewer:

Thanks @antiphp for the report!

[agones-bot]

Build Failed 😭

Build Id: d67b1d54-7d4d-41e4-a176-283019a669a5

Status: FAILURE

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[markmandel]

VERBOSE: time="2026-03-30 20:55:24.798" level=info msg="checking if GameServer exists" error="<nil>" gs=game-server58jwh state=Ready test=TestGameServerPodCompletedAfterCleanExit
VERBOSE:     gameserver_test.go:549: 
VERBOSE:         	Error Trace:	/go/src/agones.dev/agones/test/e2e/gameserver_test.go:549
VERBOSE:         	Error:      	Received unexpected error:
VERBOSE:         	            	context deadline exceeded
VERBOSE:         	Test:       	TestGameServerPodCompletedAfterCleanExit
VERBOSE: --- FAIL: TestGameServerPodCompletedAfterCleanExit (303.20s)

Got a fix for this one in #4480 (least I think so)

/gcbrun

[agones-bot]

Build Succeeded 🥳

Build Id: a05add47-7a67-49ae-94f6-84bb1cafac75

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.57.0-dev-bb349f5
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.57.0-dev-bb349f5
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.57.0-dev-bb349f5-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.57.0-dev-bb349f5
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.57.0-dev-bb349f5
• image: us-docker.pkg.dev/agones-images/ci/agones-processor:1.57.0-dev-bb349f5
• Linux C++ SDK (build): agonessdk-1.57.0-dev-bb349f5-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.57.0-dev-bb349f5.zip

A preview of the website (the last 30 builds are retained):

• https://bb349f5-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4493/head:pr_4493 && git checkout pr_4493
helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.57.0-dev-bb349f5

[lacroixthomas]

LGTM ! Good catch !