chore: add license template and headers to the files

Author: itsyaasir

.license_template

@@ -0,0 +1,2 @@
+// Copyright {20\d{2}(-20\d{2})?} IOTA Stiftung
+// SPDX-License-Identifier: Apache-2.0

LICENCE renamed to LICENSE

@@ -1,3 +1,6 @@
+// Copyright 2020-2024 IOTA Stiftung
+// SPDX-License-Identifier: Apache-2.0
+
 use thiserror::Error;
 
 pub type Result<T, E = Error> = std::result::Result<T, E>;

src/error.rs

@@ -1,3 +1,6 @@
+// Copyright 2020-2024 IOTA Stiftung
+// SPDX-License-Identifier: Apache-2.0
+
 mod error;
 mod signature_scheme;
 mod signer;

src/lib.rs

@@ -1,3 +1,6 @@
+// Copyright 2020-2024 IOTA Stiftung
+// SPDX-License-Identifier: Apache-2.0
+
 /// [`SignatureScheme`] is a trait that defines the public key and signature types.
 pub trait SignatureScheme {
     type PublicKey;

src/signature_scheme.rs

@@ -1,3 +1,6 @@
+// Copyright 2020-2024 IOTA Stiftung
+// SPDX-License-Identifier: Apache-2.0
+
 use async_trait::async_trait;
 
 use crate::Result;

src/signer.rs

@@ -1,3 +1,6 @@
+// Copyright 2020-2024 IOTA Stiftung
+// SPDX-License-Identifier: Apache-2.0
+
 use async_trait::async_trait;
 
 use crate::signature_scheme::SignatureScheme;