fix(parsing): accept list-form environment (- KEY=value) alongside map form

[Cyb3rDudu]

Compose files using the list form of environment: fail to parse. Reporter's case from #2:

services:
  registry:
    image: registry:2
    environment:
      - REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY=/data
      - REGISTRY_STORAGE_DELETE_ENABLED=true

The Compose spec allows both shapes for services.<svc>.environment:

environment:                      environment:
  KEY: value                        - KEY=value
  OTHER: value     equivalent       - OTHER=value
                                    - INHERIT_FROM_HOST

Service.swift decodes only the map form ([String: String]?), so the list form throws DecodingError.typeMismatch and the whole compose file fails to load. List form is the older docker-classic style still used by Docker Registry, Sentry, GitLab, and many other official examples — comment thread on #2 has multiple users hitting it.

Fix tries the map form first (no behavior change for existing users), falls back to a small parser:

• KEY=value splits on first = (later = chars stay in the value, so DSN-style postgres://u:p@h/db?sslmode=require round-trips)
• Bare KEY reads from ProcessInfo.processInfo.environment[KEY], falling back to empty string when unset (Compose's "inherit from host" shorthand)

Tests: 11 static cases covering both decode paths end-to-end (map form regression, list form, mixed forms across services, env key absent) plus targeted unit tests on the parseEnvironmentList helper (first-= split, DSN-style values, bare-key inheritance, duplicates, empty list).

Fixes #2. Fixes #65.