fix(client): emit typed enum for const/enum on parameter schemas

[lightsofapollo]

Summary

Follow-up to issue #10 (comment): PR #12 fixed string const inside schema components, but the parameter pipeline is a separate code path. A path/query parameter declared with { "type": "string", "const": "X" } (or enum: [...]) on its inline schema still generated impl AsRef<str>, letting callers pass any value even though only one (or a fixed set) is valid.

• ParameterInfo gains enum_values: Option<Vec<String>> (with skip_serializing_if, so existing snapshots are unchanged).
• analyze_parameter detects string-enum/const on the inline parameter schema and produces a synthetic enum type name (<OperationId><ParamName>).
• Client generator emits the inline enum with Display, AsRef<str>, an as_str() helper, and serde rename attrs — placed before the impl HttpClient block.
• Existing path/query templating (format!("{}", v) / v.to_string() for non-String rust_types) picks up the new type via Display, so no call-site changes were needed.
• Bonus: same code path also fixes explicit enum: [...] on parameter schemas, which was previously emitted as impl AsRef<str> too.

Before / after

For the issue commenter's spec:

{ "name": "the_constant", "in": "path",
  "schema": { "type": "string", "const": "MyConstantValue" } }

Before:

pub async fn some_const_operation(&self, the_constant: impl AsRef<str>) -> ...

After:

pub enum SomeConstOperationTheConstant {
    #[serde(rename = "MyConstantValue")]
    MyConstantValue,
}
// + Display, AsRef<str>, as_str() impls

pub async fn some_const_operation(
    &self,
    the_constant: SomeConstOperationTheConstant,
) -> ...

Test plan

• cargo build
• cargo test — full suite, 0 failures, no snapshot churn
• cargo fmt --check
• cargo clippy --lib -- -D warnings
• New tests/const_only_parameter_test.rs covers:
  • const-only path parameter → single-variant enum
  • enum: [...] path parameter → multi-variant enum (bonus fix)
  • const-only optional query parameter → Option<Enum>
  • Display and AsRef<str> impls are emitted

🤖 Generated with Claude Code