fix: allow not() to accept return types of and() and or()

[yosofbadr]

Summary

• Updated the not() function type signature to accept SQLWrapper | undefined (instead of just SQLWrapper) and return SQL | undefined (instead of just SQL)
• When undefined is passed (e.g. from and() or or() returning undefined), not() now returns undefined instead of producing a type error
• This makes not() composable with and() and or() without requiring type assertions

Problem

and() and or() return SQL | undefined, but not() only accepted SQLWrapper. This caused a TypeScript error when composing them:

// Type error: Argument of type 'SQL<unknown> | undefined' is not assignable to parameter of type 'SQLWrapper'.
not(and(ilike(users.name, '%asdf%')))

Fixes #1818

Test plan

• Verify not(and(...)) compiles without type errors
• Verify not(or(...)) compiles without type errors
• Verify not(undefined) returns undefined
• Verify not(someCondition) still returns SQL as before when given a defined condition
• Verify existing tests pass