Add minor util functions

[hyrodium]

Fix #198.

[codecov]

Codecov Report

Attention: Patch coverage is 84.96732% with 23 lines in your changes missing coverage. Please review.

Project coverage is 95.06%. Comparing base (61ad7eb) to head (79cb99f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/_Refinement.jl	51.61%	15 Missing ⚠️
src/_KnotVector.jl	90.74%	5 Missing ⚠️
src/_BSplineSpace.jl	90.00%	2 Missing ⚠️
src/_ChangeBasis.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #393      +/-   ##
==========================================
- Coverage   96.37%   95.06%   -1.31%     
==========================================
  Files          14       14              
  Lines        2041     2068      +27     
==========================================
- Hits         1967     1966       -1     
- Misses         74      102      +28     

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[hyrodium]

New features

• clamp, clamp!, and isclamped
  • Functions for clamped B-spline spaces and B-spline manifolds.
  • These functions are not exported not to conflict with Base.
• Base.union(k1::AbstractKnotVector, k2::AbstractKnotVector)
  • Returns k3::AbstractKnotVector, the minimum B-spline space which satisfies k1 ⊆ k3 and k2 ⊆ k3.
• Base.:+(P1::BSplineSpace{p}, P2::BSplineSpace{p})
  • Returns P3::BSplineSpace{p}, the minimum B-spline space which satisfies P1 ⊆ P3 and P2 ⊆ P3.
• knotvector
  • Add more methods
• countknots
  • Add more methods
• expand_domain
  • Experimental function without enough tests

Bug fixes

• unique(::KnotVector)
• ==(::BSplineManifold, ::RationalBSplineManifold)

Refactoring

• Add missing returns
• refinement

[hyrodium]

I chose the word "clamp" referring to https://pages.mtu.edu/~shene/COURSES/cs3621/NOTES/spline/B-spline/bspline-curve.html.