Fix/read variable size matrices and optionals

Fixes the following issues:

• reading of MatrixXf was not possible. A memory copy failed as it was assumed that the Matrix was already initialized.
• reading of std::optional in NlohmannJsonReaderWithoutTypeCheck

requested review from @peller

assigned to @reister

added 1 commit

• aa745c42 - fix redundant members, add assertions to aron generated file

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added 1 commit

• 31b05951 - using ARMARX_CHECK

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• b2fddaec - better aron assertion checking

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• c42f3fe2 - nd array reading

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approved this merge request

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• 7ba95d1b - add json export test (still WIP)

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added 2 commits

• 253040f9 - no need for special "nullopt" handling. using null instead
• b29fe086 - Merge branch 'fix/read-variable-size-matrices-and-optionals' of...

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@gao fyi

merged

mentioned in commit 5bdeb03a