Add documentation infrastructure for RTL symbols

Introduces `RtlDocEntry` and `RtlRegistration` structs to store and
manage documentation for native functions and constants. The
`Environment` struct is updated to include a registry for these
documentation entries.

The `register_native_fn` and `register_constant` methods now return an
`RtlRegistration` builder, allowing for optional chaining of `.doc()`,
`.description()`, and `.examples()` methods before the registration is
finalized when the builder is dropped.

Macros `rtl_fn!` and `rtl_const!` are introduced to simplify the
registration process with documentation.

The MCP server is extended with `get_rtl_docs` and `get_symbol_doc`
tools to expose this documentation externally.

Specific RTL functions and constants (e.g., `+`, `-`, `*`, `/`, `NaN`,
`true`, `false`, `date`, `now`, math functions, `series`, `push`, `len`,
`create-random-ohlc`, `create-ticker`, `pipe`) have been updated to
include their respective documentation using the new infrastructure.

The `Signature` and `StaticType` types have gained `to_doc_string`
methods for generating human-readable documentation strings.

src/ast/rtl/mod.rs

@@ -15,3 +15,96 @@ pub fn register(env: &Environment) {
     series::register(env);
     streams::register(env);
 }
+
+/// Registers a native RTL function and optionally attaches documentation.
+///
+/// Required: `doc:` — a short one-line description.
+/// Optional: `description:` — a longer explanation.
+/// Optional: `examples:` — a `&'static [&'static str]` of Myc code snippets.
+///
+/// # Example
+/// ```ignore
+/// rtl_fn!(env, "+",
+///     doc: "Adds two values.",
+///     add_ty, Pure, |args| { ... }
+/// );
+///
+/// rtl_fn!(env, "push",
+///     doc: "Pushes a new record into a series.",
+///     description: "The record must match the series layout.",
+///     examples: &["(push my_ticks {:price 10.5})"],
+///     push_ty, Impure, |args| { ... }
+/// );
+/// ```
+#[macro_export]
+macro_rules! rtl_fn {
+    // With description and examples
+    ($env:expr, $name:expr,
+     doc: $doc:expr,
+     description: $desc:expr,
+     examples: $ex:expr,
+     $ty:expr, $purity:expr, $impl:expr $(,)?) => {
+        $env.register_native_fn($name, $ty, $purity, $impl)
+            .doc($doc)
+            .description($desc)
+            .examples($ex);
+    };
+    // With description only
+    ($env:expr, $name:expr,
+     doc: $doc:expr,
+     description: $desc:expr,
+     $ty:expr, $purity:expr, $impl:expr $(,)?) => {
+        $env.register_native_fn($name, $ty, $purity, $impl)
+            .doc($doc)
+            .description($desc);
+    };
+    // With examples only
+    ($env:expr, $name:expr,
+     doc: $doc:expr,
+     examples: $ex:expr,
+     $ty:expr, $purity:expr, $impl:expr $(,)?) => {
+        $env.register_native_fn($name, $ty, $purity, $impl)
+            .doc($doc)
+            .examples($ex);
+    };
+    // doc only
+    ($env:expr, $name:expr,
+     doc: $doc:expr,
+     $ty:expr, $purity:expr, $impl:expr $(,)?) => {
+        $env.register_native_fn($name, $ty, $purity, $impl)
+            .doc($doc);
+    };
+}
+
+/// Registers a native RTL constant and optionally attaches documentation.
+/// Same optional fields as `rtl_fn!`.
+#[macro_export]
+macro_rules! rtl_const {
+    // With description and examples
+    ($env:expr, $name:expr,
+     doc: $doc:expr,
+     description: $desc:expr,
+     examples: $ex:expr,
+     $ty:expr, $val:expr $(,)?) => {
+        $env.register_constant($name, $ty, $val)
+            .doc($doc)
+            .description($desc)
+            .examples($ex);
+    };
+    // With description only
+    ($env:expr, $name:expr,
+     doc: $doc:expr,
+     description: $desc:expr,
+     $ty:expr, $val:expr $(,)?) => {
+        $env.register_constant($name, $ty, $val)
+            .doc($doc)
+            .description($desc);
+    };
+    // doc only
+    ($env:expr, $name:expr,
+     doc: $doc:expr,
+     $ty:expr, $val:expr $(,)?) => {
+        $env.register_constant($name, $ty, $val)
+            .doc($doc);
+    };
+}