Decode a scale file from test vectors

[pantrif]

A sample code demonstrating how to decode a scale file. Key points include:

• The file I decoded is the first one (enact-epoch-change-with-no-tickets-1.scale) from the tiny test vectors.
• All the Go structs/types conform to the types defined here.
• I wrote a test that unmarshals the scale file, writes the result to a JSON file (tests/output.json), and then compares it with the expected output.
• The entire logic served as a proof of concept (POC), so there might be some cases or types that I missed.
• All the custom marshalling logic was added solely for writing the JSON file and is not necessary.

Documentation of the library: https://github.com/ChainSafe/gossamer/tree/development/pkg/scale

Part of this: #14

UPDATE: I have added an extra file to the tests for decoding to verify the error codes.

[carlos-romano]

Is there a reason to commit chainsafe gossamer dependency to the repo?

[pantrif]

It's the library I used for decoding the scale files https://github.com/eigerco/strawberry/pull/20/files#diff-7e6ac392c29938b2f17b3da9e08256e6c4f72aec742820b6ff4cac55b307fe39R28