Merge MR !148, 'jrwrigh/newt_fluid_properties', into 'main'

refactor: Extract Newtonian fluid properties from primary Newtonian context

Closes #38

See merge request phypid/honee!148

refactor: Extract NewtonianIGProperties from NewtonianIdealGasContext

Merge branch 'jrwrigh/license_changes' into 'main'

Update License post libCEED fork

See merge request phypid/honee!6

chore: Move to Apache-2.0 OR BSD-2-Clause

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

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Merge pull request #1537 from CEED/jeremy/pragma-once

Use #pragma once for non-JiT headers

minor - update copyright headers

fluids: Implement bc_slip

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