This commit introduces the concept of "sigils," which are programmable, pure-function transformers that can be applied to a Trix container's payload.
- A `Sigil` interface with `In` and `Out` methods is defined in the `trix` package.
- The `Trix` struct now includes a `Sigils` field to attach a chain of transformers.
- The `Encode` function applies the `In` transformations before encoding the payload.
- The caller is responsible for applying the `Out` transformations after decoding.
This new feature provides a flexible and extensible data pipeline for `Trix` containers.
The implementation is fully tested with the Good, Bad, and Ugly testing strategy.
This commit refactors the test suites for the `crypt` and `trix` packages to follow the Good, Bad, and Ugly testing strategy.
- `_Good` tests cover the ideal "happy path" scenarios.
- `_Bad` tests cover expected failure scenarios with well-formed but invalid inputs.
- `_Ugly` tests cover malicious or malformed inputs designed to cause crashes or panics.
This new testing structure makes the test suite more organized, comprehensive, and robust.
Additionally, this commit includes a bug fix for the `Luhn` function, which now correctly handles empty and single-digit strings.
