[Feature Request]: Implement Decoder module (Token Generation)

### Preflight Checklist

- [x] I have read the [Contributing Guidelines](https://github.com/EnAccess/OpenPAYGO-go/blob/main/CONTRIBUTING.md) for this project, if it exists.
- [x] I agree to follow the [Code of Conduct](https://github.com/EnAccess/OpenPAYGO-go/blob/main/CODE_OF_CONDUCT.md) that this project adheres to.
- [x] I have searched the [issue tracker](https://github.com/EnAccess/OpenPAYGO-go/issues) for a feature request that matches the one I want to file, without success.

### Problem Description

To achieve support for token generation we need to have a way to encode and decode tokens. This should be used to implement an decoder, a port from the OpenPAYGO-python version. See [token_decode.py](https://github.com/EnAccess/OpenPAYGO-python/blob/main/openpaygo/token_decode.py)

### Proposed Solution

Port token decoder to Go. Check reference Above

### Alternatives Considered

No alternative solution was considered.

### Additional Information

_No response_

Start by reading the referenced openpaygo/token_decode.py in OpenPAYGO-python and inspect the OpenPAYGO-go repository structure for the appropriate package entry point. Port the decoder behavior to Go, preserving the reference implementation's token handling, and verify that the Go module can decode the same supported tokens.

Written by the indexing model from the issue text.