Small general fixes

[e-moral-sanchez]

Apply several small fixes across the library.

B-spline functions

Fix exit condition (using strict inequality) in kernel function cell_index_p when tolerance is small. This allows exporting to VTK with a prescribed grid containing exact domain bounds. More systematic use of tolerances will be applied in the future (see issue #627).

Linear algebra

• Add out argument to array_to_psydac: allow passing a PSYDAC vector to avoid allocating new memory.
• Add out argument to vec_topetsc: allow passing a PETSc.Vec object to avoid allocating new memory.
• Implement topetsc method for ZeroOperator. This also allows calling the method topetsc of a BlockLinearOperator containing ZeroOperator blocks.
• Make sure that BlockLinearOperator does not call on each block update_ghost_regions, exchange_assembly_data, remove_spurious_entries when the method does not exist (for example in case of a ZeroOperator). This error did not occur before because the zero blocks are normally just stored as None, but both possibilities should be supported.

Finite element exterior calculus

Allow using global geometric projectors with complex dtype.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 20 complexity · 17 duplication

Metric	Results
Complexity	20
Duplication	17

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🟢 Coverage 34.95% diff coverage · -0.09% coverage variation

Metric	Results
Coverage variation	✅ -0.09% coverage variation
Diff coverage	✅ 34.95% diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (f2da0cd)	51844	33084	63.81%
Head commit (24bc46e)	103924 (+52080)	66220 (+33136)	63.72% (-0.09%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#596)	186	65	34.95%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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TIP This summary will be updated as you push new changes.}

[yguclu]

Almost there! One last small request

[yguclu]

Sorry, before merging I forgot that we should update the CHANGELOG.md file, under the "Unreleased" section

[e-moral-sanchez]

I added the changes in the changelog in 08cf604