[cleanup][bugfix] Fix missing includes and one missing headerguard

See merge request !3676

Cleanup/seperate parameter group for DNM

See merge request !3679

[cleanup] Add missing content in CMakeLists.txt

See merge request !3678

[python][timeloop] avoid deprecation warnings

Closes #1311

See merge request !3681

[doc][functionfromstringexpression] Fix and simplify code example

See merge request !3680

[doc][doxygen]Symbolic representation of div and grad

See merge request !3675

Feature/std chrono parser

See merge request !3668

Feature/improve timeloop

See merge request !3648

The overload with iterators allow insertion from preexisting containers,
while the overload with std::vector allowed for a terser syntax like
`setCheckPoint({1.0, 2.0})`. But template instantiation failed with this
type of syntax because the scalar type on vector could not be deduced.

Porous-medium equations description

See merge request !3670