class Concat

StringBuilder concat handler that renders a method chain into URL path segments.

Convention:

• Bare methods become path segments: .account.whoami -> ["account", "whoami"]
• Methods with args inject the arg as a path segment after the method name: .rooms("!abc:ex.com") -> ["rooms", "!abc:ex.com"]
• .call("literal") injects a raw path segment: .("m.room.message") -> ["m.room.message"]

The handler returns an array of raw (unencoded) segments. URL-encoding is applied later when constructing the final URL.