This commit makes the magic number in the trix file format configurable.
- The `Encode` and `Decode` functions in the `trix` package now accept a `magicNumber` string as a parameter.
- The example in `examples/main.go` has been updated to demonstrate the use of the new configurable magic number.
- The tests for the `trix` package have been updated to verify the new functionality, including tests for invalid magic numbers.
This commit introduces a new, generic `.trix` file format, which is decoupled from any specific encryption algorithm.
The format is defined in `docs/trix_format.md` and consists of a magic number, version, a flexible JSON header, and a raw data payload.
A new `trix` Go package is implemented to handle the encoding and decoding of this format. Unit tests are included to verify the implementation.
An example file, `examples/main.go`, is also added to demonstrate how to use the `.trix` container to store data encrypted with the `chachapoly` package, showcasing the intended decoupled design.
