[RFC] Adding options for overriding base quantization matrices & adaptive quantizer parameters

Hi jpegli team!

I've been working on tuning jpegli for some non-standard use cases, which can greatly benefit from being able to override some of the currently hard-coded constants defined in quant.cc. This includes:

- Setting a different base quant matrix for YCbCr, the global scale and choosing a scaling mode (linear/non-linear)
- Controlling the parameters for the adaptive quantizer, at least to set `zero_bias_mul` and `zero_bias_offset`, replacing the default value of 0.5f

I've got draft version of these changes, but wanted to check there's interest to include these in the official API before starting to work on polished push requests.