fix(sdk): use ephemeral ports for Parlant servers

[darvell-thenvoi]

What changed

1. Ephemeral ports for the Parlant example servers. All five Parlant examples (01_basic_agent.py–05_jerry_agent.py) now start their in-process servers on OS-assigned ports:

async with p.Server(
    port=0,
    tool_service_port=0,
    nlp_service=p.NLPServices.openai,
) as server:
    ...

The README gains a "Running two agents locally (Tom and Jerry)" section documenting the two-terminal invocation.

2. Allow the prerelease opentelemetry-resourcedetector-gcp (CI fix). Declares that transitive package directly with a prerelease specifier in the google_adk and dev extras, plus the regenerated uv.lock.

Why

Ports: Parlant's in-process server binds a fixed default port. Starting a second Parlant agent on the same machine fails when the first still holds the port — e.g. running Tom and Jerry side by side, the second crashes with SystemExit: 1 from uvicorn startup. port=0 / tool_service_port=0 lets the OS pick free ports, so agents run concurrently. (Closes INT-530.)

Dependency: google-adk pulls opentelemetry-exporter-gcp-trace, which only depends on prerelease (alpha) builds of opentelemetry-resourcedetector-gcp. A plain, lockfile-free install excludes prereleases by default, and the sole stable build (1.13.0) was yanked upstream ("breaks imports") — so a fresh resolve of [dev]/[google_adk] has no solution. This surfaced as the packaging CI job's "Install with all extras" step failing (the test jobs pass because they use the pinned uv.lock). It affects real end users of band-sdk[google_adk], not just CI. Declaring the package with a prerelease specifier lets the resolver pick the alpha, matching what the lockfile already used.

Validation

uv run ruff check examples/parlant/*.py
uv run ruff format --check examples/parlant/*.py
uv run python -m py_compile examples/parlant/*.py
uv lock --check
# fresh wheel install, mirroring the packaging CI step:
uv build --wheel && uv pip install "dist/band_sdk-*.whl[dev]"   # resolves: resourcedetector-gcp 1.12.0a0

Notes

Rebuilt on current main. Earlier revisions of this branch carried a large Parlant rewrite plus generic-runner/docs changes; those either landed on main independently or were superseded by main's later Parlant work, so the Parlant change here is scoped to just the ephemeral-port fix.

Closes INT-530

[linear]

INT-530