Allow for a pre-built grid in `LinearFast`

[Mv77]

The CGrid constructor of the econforge interpolation library can take a substantial time if you build many interpolators.

This PR allows you to pass a pre-constructed CGrid object to LinearFast.

This can save a lot of time in instances where you are building many interpolators over the same grid. For example, if you have consumption functions for many Markov states that are defined over the same asset grid. (cc: @wdu9 ?)

• [ ] Tests for new functionality/models or Tests to reproduce the bug-fix in code.
• [x] Updated documentation of features that add new functionality.
• [x] Update CHANGELOG.md with major/minor changes.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 71.68%. Comparing base (649d8c6) to head (40dd7b3).

Files	Patch %	Lines
HARK/econforgeinterp.py	75.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1388 +/- ## ========================================== - Coverage 71.69% 71.68% -0.01% ========================================== Files 84 84 Lines 13939 13941 +2 ========================================== + Hits 9993 9994 +1 - Misses 3946 3947 +1 ```

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[alanlujan91]

This is a useful change.

However, currently interpolation.py is preventing us from moving up to python=3.12. Do you think it will be maintained and supported going forward?

[Mv77]

This is a useful change.

However, currently interpolation.py is preventing us from moving up to python=3.12. Do you think it will be maintained and supported going forward?

¯_(ツ)_/¯