feat: implement parser for FIX messages

Cargo.toml

@@ -17,3 +17,4 @@ license = "Apache-2.0"
 [workspace.dependencies]
 bytes = "1.10.1"
 insta = "1.43.2"
+thiserror = "2.0.17"

trafix-codec/Cargo.toml

@@ -10,3 +10,4 @@ license.workspace = true
 [dependencies]
 bytes.workspace = true
 insta.workspace = true
+thiserror.workspace = true

trafix-codec/src/constants/mod.rs

@@ -0,0 +1,5 @@
+/// ASCII SOH delimiter (0x01) used as field terminator in FIX messages.
+pub(crate) const SOH: u8 = b'\x01';
+
+/// ASCII equals character (=) used as delimiter between tag and value in a single field.
+pub(crate) const EQUALS: u8 = b'=';