fix: disallow complex basis vectors for now

[gdalle]

• Only allow creation of basis arrays when the eltype is a subtype of Real
• Enforce that the pushforward fallback for derivative applied to Real inputs

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.61%. Comparing base (9b17e3e) to head (e57e7ca).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ifferentiationInterface/src/misc/from_primitive.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #669   +/-   ##
=======================================
  Coverage   97.61%   97.61%           
=======================================
  Files         112      112           
  Lines        5609     5610    +1     
=======================================
+ Hits         5475     5476    +1     
  Misses        134      134           

Flag	Coverage Δ
DI	98.76% <93.33%> (+<0.01%)	⬆️
DIT	95.35% <ø> (ø)

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