Add unary operators

[linuskmr]

Add unary operators like:

• Double vertical bar |x|, e.g. for getting the length of an array or the positive value of a number
• Unary minus, e.g. -5

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May be added here as a primary expression:

fortytwo-lang/src/parser/mod.rs

Lines 634 to 641 in d1d81e1

	fn parse_primary_expression(&mut self) -> miette::Result<Expression> {
	match self.tokens.peek() {
	Some(Token { data: TokenKind::Identifier(_), .. }) => self.parse_identifier_expression(),
	Some(Token { data: TokenKind::Number(_), .. }) => Ok(Expression::Number(self.parse_number()?)),
	Some(Token { data: TokenKind::OpeningParentheses, .. }) => self.parse_parentheses(),
	Some(Token { data: TokenKind::If, .. }) => Ok(Expression::IfElse(Box::new(self.parse_if_expression()?))),
	Some(Token { data: TokenKind::For, .. }) => Ok(Expression::ForLoop(Box::new(self.parse_for_expression()?))),
	other => {