refactor: remove Iron references from docs, use const for type hash placeholder

- Remove all Iron Irwini references from book documentation (EOL Nov 2024)
- Update rmw-zenoh-rs to require Jazzy+ instead of Iron+
- Add TypeHash::TYPE_HASH_NOT_SUPPORTED const to avoid repeated string allocation
- Use const in from_rihs_string() and to_rihs_string() for consistency

Regarding serde_bridge.h:32 - comment is still accurate (returns null for Humble)

Author: YuanYuYuan

book/src/chapters/building.md

@@ -104,7 +104,7 @@ cargo build
 # For Humble - use --no-default-features
 cargo build --no-default-features --features humble
 
-# For Rolling/Iron - just add the feature
+# For Rolling/Kilted - just add the feature
 cargo build --features rolling
 ```
 

book/src/chapters/distro_compatibility.md

@@ -4,8 +4,8 @@ ros-z supports multiple ROS 2 distributions through compile-time feature flags.
 
 > **Important**: Different ros-z components have different ROS 2 version requirements:
 >
-> - **ros-z core library**: Supports Humble, Iron, Jazzy, Kilted, Rolling
-> - **rmw-zenoh-rs**: Requires Iron or later (see [rmw-zenoh-rs chapter](./rmw_zenoh_rs.md#ros-2-version-requirements))
+> - **ros-z core library**: Supports Humble, Jazzy, Kilted, Rolling
+> - **rmw-zenoh-rs**: Requires Jazzy or later (see [rmw-zenoh-rs chapter](./rmw_zenoh_rs.md#ros-2-version-requirements))
 
 ## Supported Distributions
 
@@ -24,7 +24,7 @@ ros-z supports multiple ROS 2 distributions through compile-time feature flags.
 
 The most significant difference between distributions is **type hash support**:
 
-**Jazzy/Rolling/Iron** (Modern):
+**Jazzy/Kilted/Rolling** (Modern):
 
 - Supports real type hashes computed from message definitions
 - Format: `RIHS01_<64-hex-chars>` (ROS IDL Hash Standard version 1)

book/src/chapters/rmw_zenoh_rs.md

@@ -35,21 +35,21 @@ ROS 2 uses a middleware abstraction layer called RMW (ROS Middleware) that allow
 ### ROS 2 Version Requirements
 
 ```admonish warning title="Humble Not Supported"
-rmw-zenoh-rs requires **ROS 2 Iron (2023) or later**.
+rmw-zenoh-rs requires **ROS 2 Jazzy (2023) or later**.
 ROS 2 Humble (2022 LTS) is **not supported**.
 ```
 
 **Supported ROS 2 Distributions:**
 
-- ✅ **Iron** (2023)
+- ✅ **Jazzy** (2023)
 - ✅ **Jazzy** (2024 LTS) - Recommended
 - ✅ **Kilted** (2025)
 - ✅ **Rolling**
 - ❌ **Humble** (2022 LTS) - See [Why No Humble Support?](#why-no-humble-support)
 
 ### System Requirements
 
-- **ROS 2 Iron or later** (Jazzy recommended)
+- **ROS 2 Jazzy or later** (Jazzy recommended)
 - **Rust toolchain** (1.91 or later)
 - **Cargo** (comes with Rust)
 - **CMake** (3.16 or later)
@@ -154,7 +154,7 @@ The router runs as a separate process and manages discovery and routing between
 
 ## Why No Humble Support?
 
-ROS 2 Iron (May 2023) introduced **breaking changes to the RMW API** that are fundamental to how rmw-zenoh-rs works. These are not minor API additions - they are architectural changes defined in ROS Enhancement Proposals (REPs).
+ROS 2 Jazzy (May 2023) introduced **breaking changes to the RMW API** that are fundamental to how rmw-zenoh-rs works. These are not minor API additions - they are architectural changes defined in ROS Enhancement Proposals (REPs).
 
 ### Missing APIs in Humble
 
@@ -173,7 +173,7 @@ rmw-zenoh-rs uses type hashes as part of Zenoh key expressions for topic matchin
 **Example:**
 
 ```text
-Iron+ Key: /topic/String/RIHS01_<64-char-hash>/...
+Jazzy+ Key: /topic/String/RIHS01_<64-char-hash>/...
 Humble:    Cannot generate proper type hash
 ```
 
@@ -194,7 +194,7 @@ Used for network optimization and selective discovery in distributed systems.
 **What's Missing:**
 
 - Humble uses FastCDR v1.x
-- Iron+ uses FastCDR v2.x
+- Jazzy+ uses FastCDR v2.x
 - Constructor signatures incompatible
 
 #### 4. Additional Missing Features
@@ -258,7 +258,7 @@ Both `rmw_zenoh_rs` and `rmw_zenoh_cpp` are RMW implementations using Zenoh, but
 |---------|--------------|---------------|
 | **Implementation Language** | Rust (using ros-z) | C++ |
 | **Primary Use Case** | Integration with ros-z ecosystem | Standalone Zenoh RMW |
-| **ROS 2 Compatibility** | Iron, Jazzy, Kilted, Rolling | Humble, Iron, Jazzy, Kilted, Rolling |
+| **ROS 2 Compatibility** | Jazzy, Jazzy, Kilted, Rolling | Humble, Jazzy, Jazzy, Kilted, Rolling |
 | **Humble Support** | ❌ No | ✅ Yes |
 | **Status** | Experimental | Production-ready |
 | **Dependencies** | ros-z, Zenoh Rust | Zenoh C++ binding |

crates/ros-z-protocol/src/entity.rs

@@ -130,6 +130,9 @@ pub struct TypeHash {
 }
 
 impl TypeHash {
+    /// Placeholder value for type hash when not supported (ROS 2 Humble)
+    const TYPE_HASH_NOT_SUPPORTED: &'static str = "TypeHashNotSupported";
+
     pub const fn new(version: u8, value: [u8; 32]) -> Self {
         Self { version, value }
     }
@@ -143,7 +146,7 @@ impl TypeHash {
 
     pub fn from_rihs_string(rihs_str: &str) -> Option<Self> {
         // Handle ROS 2 Humble's "not supported" placeholder
-        if rihs_str == "TypeHashNotSupported" {
+        if rihs_str == Self::TYPE_HASH_NOT_SUPPORTED {
             return Some(TypeHash::zero());
         }
 
@@ -174,7 +177,7 @@ impl TypeHash {
         #[cfg(feature = "no-type-hash")]
         {
             // ROS 2 Humble doesn't support type hashing
-            "TypeHashNotSupported".to_string()
+            Self::TYPE_HASH_NOT_SUPPORTED.to_string()
         }
 
         #[cfg(not(feature = "no-type-hash"))]