feat: add ledgerflow-sdk crate with signed merchant API client and webhook verification

Author: Akagi201

crates/ledgerflow-sdk/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "ledgerflow-sdk"
+version.workspace = true
+edition.workspace = true
+
+[package.metadata.cargo-shear]
+ignored = []
+
+[dependencies]
+hmac = "0.13.0"
+hpx.workspace = true
+serde = { workspace = true, features = ["derive"] }
+serde_json.workspace = true
+sha2.workspace = true
+thiserror.workspace = true
+
+[lints]
+workspace = true