Fix Solidity warnings

[cgewecke]

Preliminary step for upgrading Solidity at some point in the future. It's common for warnings to become errors at the solc version increases.

Removes a few dozen warnings, in 3 categories.

• Missing SPDX license id
• state mutability can be restricted to pure or view (mostly in mocks and adapters)
• unused parameters

Only changes that touch logic are in

• 788d040 where a NavIssuance module internal method has an unused parameter
• 34e6e76 where an unused local variable assignment is made in CompoundLeverageModule

(Also removed a lot of trailing whitespace here ... there's a bit of noise in the diff unfortunately)