test: migrate stable compose run tests to nerdtest framework

Migrates the non-flaky compose run tests to nerdtest.Setup():
- TestComposeRunWithEnv
- TestComposeRunWithUser
- TestComposeRunWithArgs
- TestComposeRunWithEntrypoint
- TestComposeRunWithLabel (uses nerdtest.InspectContainer)
- TestComposeRunWithVolume (uses nerdtest.InspectContainer)

Replaces the unbuffer(1) pty wrapper with cmd.WithPseudoTTY(), and
uses expect.ExitCodeSuccess instead of literal 0 for exit codes.

TestComposeRunWithServicePorts, TestComposeRunWithPublish, and
TestComposePushAndPullWithCosignVerify are intentionally left on the
legacy framework for now (flaky / complex).

Author: sathiraumesh