fix(compose): support explicit network names

[x3ccd4828]

Summary

• accept the Compose name field on top-level network definitions
• emit the explicit name as NetworkName= in the generated Quadlet network unit
• add regression coverage for the conversion

Why

Compose allows a network resource key and the created network's name to differ:

networks:
  backend:
    name: explicit-network-name

Podlet 0.3.2 currently rejects this input because the Quadlet network conversion classifies name as unsupported. Mapping it to NetworkName= preserves the resource key for the generated backend.network file and its container references while creating the Podman network with the requested explicit name.

This implements the behavior described in #21.

Validation

• cargo fmt --verbose --check
• cargo clippy -- -Dwarnings
• cargo test --verbose (78 passed)
• end-to-end Compose conversion confirmed Network=backend.network and NetworkName=explicit-network-name