emu-docker create: add --name flag to override generated image name

[jpcottin]

Why

emu-docker create auto-generates image names like 36-google-x64-ps16k from system image properties. Sensible default, but doesn't fit deployments that have their own image-naming convention (e.g., prod-emu-android16, or matching an internal registry's path layout).

Change

Adds a --name flag to emu-docker create that overrides the auto-generated image name. When unset, behavior is unchanged.

emu-docker create stable "Q google_apis x86_64" --name my-custom-image-name

Credit

Rebase + extraction of @gregersn's #359, which bundled this with an unrelated ANDROID_REPOSITORY env-var feature. Splitting into two PRs (this one + a follow-up for the repository override). Original commit authored 2021-11-04; preserved here as Author: Greger Stolt Nilsen <greger@fusetools.com> via cherry-pick onto current master. No code changes from the original — clean cherry-pick, no rebase conflicts.

Test plan

• All 42 existing unit tests pass (pytest tests/ --ignore=tests/e2e) on the cherry-picked commit
• emu-docker create --help lists --name NAME Name to give image when pushed.
• EmulatorContainer.image_name() returns the override when self.name is set
• name=None (the default) preserves the existing <sdk>-<tag>-<cpu> auto-generation path (covered by existing unit tests)
• CI from ci: add GitHub Actions workflow to run pytest on PRs #405 reruns the matrix (Python 3.10/3.11/3.12/3.13)

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