feat(libsy): expose Python algorithm execution

[nachiketb-nvidia]

Stack

1. feat(libsy): expose typed Python protocol bindings #88 Protocol bindings
2. feat(libsy): expose Python target bindings #89 Target bindings
3. feat(libsy): expose Python algorithm execution #87 Algorithm execution (this PR)
4. feat(libsy): expose Python run streams #82 Host-driven run streams

Review after #89.

Why

Python hosts need to run Rust-owned algorithms using configured target clients without exposing algorithm implementation or subclassing hooks.

What

• Add an opaque Algorithm handle with run().
• Add noop() and random(targets) factories.
• Add typed Decision values and the RoutedLlmClient protocol.
• Adapt Python async clients to the Rust RoutedLlmClient trait.
• Convert target sets into Rust-owned snapshots at factory construction.
• Add no-op, random-routing, and client-error tests.

How

The adapter releases Python while awaiting the host client and maps the typed response back into the Rust protocol. Algorithm implementations remain Rust-owned and factories return one shared handle type.

What to review

1. Opaque algorithm and factory API.
2. Python client adapter and error propagation.
3. Target snapshot semantics.
4. Context, request, decision, and response conversions.

Validation

• cargo fmt --all -- --check
• cargo clippy -p switchyard-py --all-targets -- -D warnings
• uv run pytest the protocol, target, and algorithm binding tests (13 passed)