Contract code cleanup and unit tests

[aalavandhan]

• Removed all string require errors in favor of solidity custom errors
• Updated fee policy interface with redundant computeDeviationRatio methods
• Perp interface cleanup, skipping update state when system is paused
• Vault interface cleanup, caching and dust handling
• Unit tests

[brandoniles]

For the first commit, bccbb8b

[brandoniles]

For #2, 5c12093

[brandoniles]

For #3, ce60170

[brandoniles]

For #4, e0b74e5

[brandoniles]

For #5, 294b89e

[brandoniles]

LGTM

Do you know the code coverage after these unit tests?

[aalavandhan]

Should be pretty close to 100%.. we'll know when the ci runs