refactor(fluids): Make QF comments consistent

See discussion: https://github.com/CEED/libCEED/pull/1539#discussion_r1548312418

fluids: Misc style changes

fluids: Make BCs compatible with explicit TS

Drop JiT Guards in Most QF Source (#1540)

* backend - use pragma once

* gallery - drop source header guards

* ex - drop some qfunction source header guards

* fluids - drop guards on all sin

Drop JiT Guards in Most QF Source (#1540)

* backend - use pragma once

* gallery - drop source header guards

* ex - drop some qfunction source header guards

* fluids - drop guards on all singly included headers

* jit - drop most guards on backend JiT files

* sycl - drop extra header guards

* jit - enable #pragma once for QF source

* fluids - use #pragma once for util/helper qf source

* test - check different multiple includes

* fluids - fix odd include

* jit - update interface for building JiT string from multiple files

show more ...

minor - update copyright headers

fluids: Test zbox in SmartSim test

This tests whether the output training data handles multiplicity
correctly. And also is the first fluids test with zbox.

fluids: Add GetInverseMultiplicity

fix(fluids): RHS stabilization term should be negative

fluids: Add different tau choices for advection

fluids: Implement bc_slip

This is a weak version of slip boundary condition based on a Riemann
solve

fluids: Implement sequential SGS DD eval

fluids: Add QFs for external SGS DD evaluation

fluids: Refactor function names

- PascalCase for acronyms longer than 2 letters
- Remove the "Anisotropic" qualifier from function names, as we only
have one data-driven SGS model. If we add an is

fluids: Refactor function names

- PascalCase for acronyms longer than 2 letters
- Remove the "Anisotropic" qualifier from function names, as we only
have one data-driven SGS model. If we add an isotropic model later, we
can give that the "Isotropic" qualifier on it's function names
- Remove the "Model" qualifier from function names. "SgsDD" is
communicative enough (Subgrid-stress inherently means a model)

show more ...

fluids: Change SGS IFunctionApply to use NewtonianIdealGasContext

- It doesn't need anything more than that

fluids: Create generic SGS DD eval interface

- Existing implementation now called "Fused" evaluation

fluids: Use utility for velocity gradient projection

- Evidentily missed this one when I added
StatePhysicalGradientFromReference awhile back. Or this was on a
longer lived branch that got me

fluids: Use utility for velocity gradient projection

- Evidentily missed this one when I added
StatePhysicalGradientFromReference awhile back. Or this was on a
longer lived branch that got merged out-of-order

show more ...

fluids: Merge 2D and 3D advection setup

Instead of `-problem advection` and `-problem advection2d`, there's just
`-problem advection` and the dimensionality is taken from the dm.

fluids: Generalize advection boundary qfunctions

fluids: Packing routines for 2D boundary setup

fluids: Generalize advection RHSFunction for 2d and 3d

fluids: Convert strong_form to boolean in advection

fluids: Generalize advection IFunction for 2d and 3d

fluids: Change 2D qdata to use unpacking routines

fluids: Generalize advection IC for 2d and 3d

fluids: Create generic MatMatN for square matrices

MatMat3 now uses MatMatN