Bump TaylorSeries to v0.21

[schillic]

Closes #189.
I copied the changes from ed01548 to make the tests pass.

[lbenet]

Thanks @schillic! LGTM. Merging (and then tagging).

[lbenet]

Do you also need a new release?

[schillic]

Yes, the hope was that you could release this earlier without pressure in #189.

[lbenet]

A new patch version, or a minor version?

[schillic]

Whatever you think it should be 😃

[lbenet]

The big changes in TaylorSeries v0.21 is using FixedSizeArrays (for storing the coefficients) instead of Vectors. This improves the performance regresions somehow introduced in Julia v1.11 and 1.12 vs Julia 1.10. So, I guess a minor version is worth.

[lbenet]

I tagged a patch version... sorry for the mistake...

[lbenet]

(It's not good to work on easter sunday)

[schillic]

For me it is not a problem. It actually saves time because now there are fewer CompatHelper messages :)

[schillic]

Actually, the version could be considered breaking if you access the internals of TaylorN etc. Now you need to use get_order.

[lbenet]

Let's leave like that then...

[schillic]

We cannot change it anyway 😉