refactor: use # for private methods to reduce the minified file size

[Master-Hash]

This PR reduces the bundle size using # for the private properties instead of the private keyword when the code is minified.

The results of esbuild ./rapier.js --bundle --minify --target=esnext --format=esm --outfile=out.js:

-a---          2025/10/23    19:36         112241 old.js
-a---          2025/10/23    20:12         111075 new.js

which is about 1.04% smaller. If you can find more private methods/property, It can be even smaller.

The principle is explained here.

The PR is tested on my own app.

[krutoo]

But you also replaced protected members - this is wrong because now you can use it in child classes

[Master-Hash]

But you also replaced protected members - this is wrong because now you can use it in child classes

It causes no runtime error. I'm not sure whether it should be private or protected: if you are sure, I'll revert it.

[krutoo]

It causes no runtime error. I'm not sure whether it should be private or protected: if you are sure, I'll revert it.

To be honest, I'm not sure either (the library author decides), but protected and private access modifers in TypeScript is needed not for runtime but for compile time to declare bounds of fields access when working with a class and its instances