Set opt-level z (#353)

Set opt-level to `z` and enable _fat_ `lto`.

From testing this seems to result in a minimal performance decrease.
Decrypting a vault of 2000 items in wasm goes from 1470ms to ~1500ms.
While the `.wasm` filesize decreases from 3.5M to 1.9M.

Author: Hinton

Cargo.toml

@@ -104,8 +104,9 @@ opt-level = 1
 
 # Turn on LTO on release mode
 [profile.release]
-lto = "thin"
 codegen-units = 1
+lto = true
+opt-level = "z"
 
 # Stripping the binary reduces the size by ~30%, but the stacktraces won't be usable anymore.
 # This is fine as long as we don't have any unhandled panics, but let's keep it disabled for now