feat: move uncommon functions over from Lux

[avik-pal]

Moves over these

• [x] adds PeriodicEmbedding
  • [x] implementation
  • [x] documentation
  • [x] testing
• [x] adds DynamicExpressionsLayer
  • [x] implementation
  • [x] documentation
  • [x] testing
• [x] adds the SymbolicRegression tutorial over from Lux docs and remove the tutorial there, linking this repo.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 83.33333% with 19 lines in your changes missing coverage. Please review.

Project coverage is 90.06%. Comparing base (b780a45) to head (35bcf45).

Files	Patch %	Lines
ext/BoltzDynamicExpressionsExt.jl	88.73%	8 Missing :warning:
src/layers/dynamic_expressions.jl	75.86%	7 Missing :warning:
src/layers/periodic_embedding.jl	69.23%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #48 +/- ## ========================================== - Coverage 92.33% 90.06% -2.27% ========================================== Files 22 25 +3 Lines 339 453 +114 ========================================== + Hits 313 408 +95 - Misses 26 45 +19 ```

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