feat: Add python-uv template

[vdusek]

Description

Adds a python-uv Actor template - an example of building and running Actors with the uv package and project manager:

• pyproject.toml + committed uv.lock and .python-version, so local development and the platform Docker build use identical dependency versions,
• a uv-based Dockerfile (uv binary from its official image, uv sync --locked --no-dev in a cached dependency layer),
• the same single-page heading scraper as python-start (HTTPX + BeautifulSoup), so the two templates are directly comparable - only the project management differs,
• uv-aware .gitignore/.dockerignore (keep uv.lock and .python-version committed, never ship .venv).

Infrastructure changes:

• test/templates.test.js: checkPythonTemplate now dispatches on the presence of uv.lock - uv-based templates install dependencies via uv sync --upgrade (mirroring the requirements.txt flow, which also always installs the latest allowed versions) and the latest-SDK assertion stays in place. The pip flow is unchanged.
• test_python_templates.yaml: added astral-sh/setup-uv (without a Python version input, so the template's .python-version stays authoritative).

Verified locally: the jest template test passes for python-uv (structure, uv install + latest-SDK check, apify run scrapes and exits 0), python-empty passes as a pip-flow control, and the Docker image builds and runs end to end. The dist archive is intentionally not included - the master automation builds and commits it after merge.

Known limitation: apify create currently hard-codes pip install -r requirements.txt for Python templates, so creating this template via the CLI errors after extraction (the project folder survives and uv sync + apify run work fine - apify run already picks up the uv-created .venv). The manifest's postCreate message points users at uv sync, and --skip-dependency-install avoids the error entirely. A follow-up in apify/apify-cli (run uv sync when uv.lock is present) would close this gap.

Companion documentation PR: apify/apify-sdk-python#932 (new "Use uv" SDK guide linking this template).

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