[Internals] Internalize integration routines

[lrnv]

To be able to ditch HCubtature.jl and thus StaticArrays.jl, which increase load time. Hopefully without performance losses ? Not sure yet.

This work but its awfully slow, but maybe we can make it faster there are probably inneficinecies all around this implementation we"'ll have to rpoof-èread it.

Not sure I want to merge it.

[codecov]

Codecov Report

❌ Patch coverage is 98.47716% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.71%. Comparing base (c974872) to head (981167d).

Files with missing lines	Patch %	Lines
src/hcubature.jl	98.34%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #340      +/-   ##
==========================================
+ Coverage   77.95%   78.71%   +0.75%     
==========================================
  Files          84       85       +1     
  Lines        4986     5178     +192     
==========================================
+ Hits         3887     4076     +189     
- Misses       1099     1102       +3     

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