New version: Clapeyron v0.6.21

[JuliaRegistrator]

• Registering package: Clapeyron
• Repository: https://github.com/ClapeyronThermo/Clapeyron.jl
• Created by: @longemen3000
• Version: v0.6.21
• Commit: 886f5eba39d1fc37d9e8850915bafb002f3263ad
• Reviewed by: @longemen3000
• Reference: ClapeyronThermo/Clapeyron.jl@886f5eb#commitcomment-176629537
• Description: Clapeyron provides a framework for the development and use of fluid-thermodynamic models, including SAFT, cubic, activity, multi-parameter, and COSMO-SAC.
• Release notes:

# v0.6.21

## New Features

- Python: official python wrapper, available in pypi: [pyclapeyron](https://pypi.org/project/pyclapeyron/). 
- `GroupParam` can now store non-integer values.
- `MultiPhaseTPFlash`: support for Gamma-Phi models
- Cubics: translation now does not allocate in most cases.
- New model: translated industrial PC-SAFT (`iPCSAFT`)
- New model: VTPR with temperature-dependent translation (`TVTPR`)
- Electrolyte models: `mean_ionic_activity_coefficient` and `osmotic_coefficient` (and their saturated variants), can now be called directly without specifying salts, if the model forms binary salts. For example, (`osmotic_coefficient(model,p,T,m)`) is equivalent to(`osmotic_coefficient(model,salts,p,T,m)`), where `salts = Clapeyron.auto_binary_salts(model)`
- `DHModel`: improved numerical stability of `a_dh` when the electrolyte concentrations are small.
- association options can now be initialized directly from a symbol: (`PCSAFT(["water","ethanol"],assoc_options = :cr1)`)

## package deprecations

- JSON3.jl was removed in favour of JSON.jl

## Bug fixes

- `AntoineSaturation` now uses SI units
- Fixes in `PenelouxTranslation` (inverted parameters for PR and RK models)
- Patel-Teja: the correlation for ζc is used first instead of the experimental critical volume
- Various documentation improvements
- Fixed precompilation errors in `ClapeyronSymbolicsExt`

[github-actions]

Hello, I am an automated registration bot. I help manage the registration process by checking your registration against a set of AutoMerge guidelines. If all these guidelines are met, this pull request will be merged automatically, completing your registration. It is strongly recommended to follow the guidelines, since otherwise the pull request needs to be manually reviewed and merged by a human.

1. AutoMerge Guidelines are all met! ✅

Your new version registration met all of the guidelines for auto-merging and is scheduled to be merged in the next round (~20 minutes).

2. To pause or stop registration

If you want to prevent this pull request from being auto-merged, simply leave a comment. If you want to post a comment without blocking auto-merging, you must include the text [noblock] in your comment.

Tip: You can edit blocking comments to add [noblock] in order to unblock auto-merging.