chore: drop dead Cargo.lock from package exclude list

cargo always includes a git-tracked lockfile in the package regardless
of the exclude entry; keeping it listed implied a behavior that does not
exist.

Cargo.toml

@@ -9,7 +9,7 @@ readme = "README.md"
 repository = "https://git.alk.dev/alkdev/alkcall"
 keywords = ["rpc", "json-rpc", "multiplexing", "wire-format", "alpn"]
 categories = ["network-programming", "asynchronous", "encoding"]
-exclude = [".opencode/", "AGENTS.md", "docs/reviews/", "docs/sdd_process.md", "Cargo.lock"]
+exclude = [".opencode/", "AGENTS.md", "docs/reviews/", "docs/sdd_process.md"]
 
 [lib]
 name = "alkcall"