SGS model updates

[timofeymukha]

Final cherry-pick from stress_formulation.

• Introduces 2 ways to compute the LES filter width. Currently, just an if statement. We should probably upgrade to have a factory and types later.
• Averages the strain-rate values at the element boundaries before using them to compute eddy viscosity.
• Some fixes to filtering that @Shiyu-Sandy-Du knows about :P.

[timofeymukha]

The linter strikes again :D. I gotta say ,I am loving this

[njansson]

The linter strikes again :D. I gotta say ,I am loving this

I'm happy to have admin permission, and can bypass all rules :D

[timofeymukha]

@Shiyu-Sandy-Du what needs to be done is to go through the files in the les directory like, for example, this flint lint -r flinter_rc.yml src/les/les_model.f90 and address the complaints.

[njansson]

@Shiyu-Sandy-Du what needs to be done is to go through the files in the les directory like, for example, this flint lint -r flinter_rc.yml src/les/les_model.f90 and address the complaints.

kitten atrocities! But for a good cause (^-^)v

[Shiyu-Sandy-Du]

Finally!