Integer bounds handling

[jonasstrehle]

Core team (@janiejestemja, @benStre and @jonasstrehle) considered on we need to allow -10u8 syntax in DATEX.
Overflow can occur at runtime, in any case, so definition should be also allowed - next to that expression is handled as unary operations, not as lexer. So we could think of showing some warning on -10u8 or type x: integer/u8 = 10 syntax if we want.

var x: integer/u8 = 1000 // <integer>1000 will be cast down to u8
var x: integer/u8 = -10 // <integer>-10 cast to u8 (sign bit )

var x: integer/u8 = -10 * 100 // calculation in integer space -> -1000 then cast to u8 -> 24
// vs
var x: integer/u8 = -10u8 * 100u8 // both are cast to u8 first -> (246 * 100) -> whatever