Add implicit query builder conversions from bool to BoolExpr

[joshua-spacetime]

Description of Changes

Adds implicit query builder conversions from bool to BoolExpr so that you can write:

ctx.from.user().r#where(|u| u.online)

instead of

ctx.from.user().r#where(|u| u.online.eq(true))

Also removes NullableCol and NullableIxCol types from C# query builder.

API and ABI breaking changes

None

Expected complexity level and risk

1

Testing

Unit and smoketests

[Shubham8287]

Reviewed for Rust and Typescript, looks great.