Implement Error and Display traits for Error enum.

Also implement From<Error> for i32.

Change-Id: I6d63a4d61013c014d58ada6c396d0e8108f9bbc1
Signed-off-by: Andrew Walbran <qwandor@google.com>
diff --git a/Cargo.toml b/Cargo.toml
index 90ed22a..cecea86 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,4 +16,5 @@
 
 [dependencies]
 num_enum = { version = "0.7", default-features = false }
+thiserror = { version = "2.0.3", default-features = false }
 uuid = { version = "1.10", default-features = false }