fix(compiler): Fix math ops for u64 [fixes LNG-204]

[InversionSpaces]

No description provided.

[linear]

LNG-204 Fix math for `u64` type

Now it is impossible to use u64 in mathematical operations:

func getU64() -> u64:
    <- 42

func main():
    a <- getU64()
    b <- getU64()
    c = a + b

output:

7     c = a + b
          ^====
          Types mismatch.
          expected:   i64
          given:      u64

[InversionSpaces]

Made literal numbers without sign (e.g. 42) to have LiteralType.unsgined instead of LiteralType.number.
Note that LiteralType.unsigned includes signed types. Logic is that literal without sign could have type with sign.
However LiteralType.signed and LiteralType.unsgined do not include float despite that they could be treated as floats.

I don't like idea of literal types in general, and propagating them through expressions (e.g. 42 + 37 has LiteralType.unsigned) creates a lot of troubles