feat(project): Establish initial IRTT workspace and protocol definitions

Set up the multi-crate project structure and add the core IRTT protocol with pinned dependencies for reproducible builds.

crates/irtt-proto/src/flags.rs

@@ -0,0 +1,20 @@
+use crate::{error::Result, ProtoError};
+
+pub const FLAG_OPEN: u8 = 0x01;
+pub const FLAG_REPLY: u8 = 0x02;
+pub const FLAG_CLOSE: u8 = 0x04;
+pub const FLAG_HMAC: u8 = 0x08;
+
+pub const RESERVED_FLAGS_MASK: u8 = 0xF0;
+
+pub fn validate_flags(flags: u8) -> Result<()> {
+    let reserved = flags & RESERVED_FLAGS_MASK;
+    if reserved != 0 {
+        return Err(ProtoError::ReservedFlags(reserved));
+    }
+    Ok(())
+}
+
+pub fn has(flags: u8, flag: u8) -> bool {
+    flags & flag != 0
+}