all: add missing copyright headers

Tests are CC0/public domain because there's no reason for them not to
be. Examples are also CC0/public domain, but this may be a little bit
weird because they are largely straightforward ports of examples from
nats.c which carry the Apache license. However, I personally wrote
them against the zig bindings and I doubt anyone will end up in a
court of law due to their software containing uselessly trivial
example code.

src/connection.zig

@@ -1,3 +1,17 @@
+// Copyright 2023 torque@epicyclic.dev
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 const std = @import("std");
 
 pub const nats_c = @cImport({

src/error.zig

@@ -1,3 +1,17 @@
+// Copyright 2023 torque@epicyclic.dev
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 const std = @import("std");
 
 pub const nats_c = @cImport({

src/message.zig

@@ -1,3 +1,17 @@
+// Copyright 2023 torque@epicyclic.dev
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 const std = @import("std");
 
 pub const nats_c = @cImport({

src/statistics.zig

@@ -1,3 +1,17 @@
+// Copyright 2023 torque@epicyclic.dev
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 const std = @import("std");
 
 const nats_c = @cImport({

src/subscription.zig

@@ -1,3 +1,17 @@
+// Copyright 2023 torque@epicyclic.dev
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 const std = @import("std");
 
 pub const nats_c = @cImport({

src/thunk.zig

@@ -1,3 +1,17 @@
+// Copyright 2023 torque@epicyclic.dev
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 const std = @import("std");
 
 pub const nats_c = @cImport({