chore: move windows from tier 3 to unsupported

[aaronbuchwald]

Why this should be merged

This PR moves Windows from Tier 3 support to Unsupported according to the support tiers outlined in the README.

How this was tested

CI

Need to be documented in RELEASES.md?

Yes.

Notes on Retained Windows Specific Support

Opted to leave windows specific support in place rather than remove it in this PR because the intent is to downgrade the guarantee of support, but this does not mean we need to remove the existing windows specific support. If preferred, we can remove all windows specific handling as well.

The following files contain windows specific handling or references based on a search of the codebase:

• avalanchego/vms/rpcchainvm/runtime/subprocess/linux_stopper.go

  Line 7 in 092cf18

  // ^ SIGTERM signal is not available on Windows

• avalanchego/utils/ulimit/ulimit_windows.go

  Line 13 in 092cf18

  // Set is a no-op for windows and will warn if the default is not used.

• avalanchego/utils/storage/storage_windows.go

  Line 4 in 092cf18

  //go:build windows

• avalanchego/utils/perms/write_file.go

  Line 15 in 092cf18

  // ioutil.WriteFile on windows.

• avalanchego/tests/fixture/tmpnet/detached_process_windows.go

  Line 11 in 092cf18

  panic("tmpnet deployment to windows is not supported")

• https://github.com/ava-labs/avalanchego/blob/092cf182dd92b66a8ab882b657d3ae52b174c913/tests/fixture/tmpnet/README.md#package-details

[Copilot]

Pull Request Overview

This PR downgrades Windows support from Tier 3 to unsupported, removes Windows-specific CI steps, and cleans up the related workflow file.

• Update Windows support tier in the README
• Remove Windows runner and timeout in CI matrix
• Delete the standalone Windows build workflow and its lint exception

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
scripts/actionlint.sh	Removed the skip rule for the now-deleted Windows build workflow
README.md	Changed Windows support tier from “3” to “Not supported”
.github/workflows/ci.yml	Excluded windows-2022 from the test matrix and removed its timeout setting
.github/workflows/build-win-release.yml	Deleted the Windows release build workflow

[maru-ava]

Do we also want to remove usage of go:build windows?

I see that's handled separately by #4032

[StephenButtolph]

lgtm. Will wait to see if there is any pushback

[aaronbuchwald]

Do we also want to remove usage of go:build windows?

I see that's handled separately by #4032

Ya I split these out into two as I thought this was the minimum changes needed to deprecate official windows support ie. testing and generating releases. The follow on is if we also want to delete the work we've done, so that it can run on windows, which I don't think is strictly necessary.