nullable timestamptz support (`Date | null`)

[timvandam]

Describe the bug
A clear and concise description of what the bug is.

Currently inserting/updating nullable timestamptz values in postgres don't work. Using variables of type Date | null causes error ESLint: Invalid Query: Unsupported union type(@ts-safeql/ check-sql)

To Reproduce
Steps to reproduce the behavior:

Make a table with a nullable timestamptz column and try to insert a Date | null value

Expected behavior
A clear and concise description of what you expected to happen.

It should work

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. iOS]
• PostgreSQL version [e.g. 13, 14]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.

I may have some time to try to fix this over the weekend

[karlhorky]

@timvandam If you can provide a reproduction in this format with the table schema, sql tag and ESLint error, that would be helpful to understand the problem:

CREATE TABLE users (
  -- ...
)

// 💥 Query has incorrect type annotation.
//	Expected: { has_private_url: boolean; }
//	Actual: { has_private_url: boolean | null; }[]
await sql<{ has_private_url: boolean }[]>`
  SELECT
    ${true} AS has_private_url
  FROM
    users
`;