Update capabilities to be expressible by Boolean literals

[mattt]

Related to #12

Before

let server = Server(
    name: "TestServer",
    version: "1.0.0",
    capabilities: .init(
        prompts: .init(),
        resources: .init(),
        tools: .init()
    )
)

---

After

let server = Server(
    name: "TestServer",
    version: "1.0.0",
    capabilities: .init(
        prompts: true,
        resources: true,
        tools: true
    )
)