Move CodexAuth and AuthManager to the core crate (#3074)

Fix a long standing layering issue.

codex-rs/Cargo.lock

@@ -665,7 +665,7 @@ dependencies = [
  "clap",
  "codex-common",
  "codex-core",
- "codex-login",
+ "codex-protocol",
  "reqwest",
  "serde",
  "serde_json",
@@ -718,7 +718,6 @@ dependencies = [
  "bytes",
  "chrono",
  "codex-apply-patch",
- "codex-login",
  "codex-mcp-client",
  "codex-protocol",
  "core_test_support",
@@ -847,6 +846,7 @@ version = "0.0.0"
 dependencies = [
  "base64 0.22.1",
  "chrono",
+ "codex-core",
  "codex-protocol",
  "pretty_assertions",
  "rand 0.8.5",