Port alknet-typedef crate from alknet

Copy the binary struct engine (src/, tests/) verbatim from
alknet/crates/alknet-typedef and create a standalone Cargo.toml
(workspace-inherited fields inlined). Port the architecture docs
(specs, ADRs 095-102, OQs 069-071) from alknet's nested multi-crate
layout to a flat single-crate layout, fixing relative link paths.

Build, 295 tests, and clippy all pass clean.

Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "alknet-typedef"
+version = "0.1.0"
+edition = "2021"
+license = "MIT OR Apache-2.0"
+description = "Binary struct engine: takes a JSON Schema with TypeDef:* custom keywords and produces an offset map, read/write functions, and validation"
+repository = "https://git.alk.dev/alkdev/alktype"
+
+[lib]
+name = "alknet_typedef"
+
+[features]
+default = []
+
+[dependencies]
+jsonschema = { version = "0.46", default-features = false }
+serde_json = { version = "1", features = ["preserve_order"] }