fix(fstring): display absolute value of int after sign

examples/basic/23_format_spec.peb

@@ -12,6 +12,12 @@ print(f"{c:,._}")
 print(f"{c:_.,}")
 
 // Sign
+let d1 = 14
+let d2 = -26
+print(f"{d1} {d2}")
+print(f"{d1:+} {d2:+}")
+print(f"{d1:-} {d2:-}")
+print(f"{d1: } {d2: }")
 
 // Percentage
 let pts = 19
@@ -19,5 +25,9 @@ let total = 22
 print(f"Correct answers: {pts/total:.2%}")
 
 // Precision
+print(f"{c:8}")
+print(f"{c:8.2}")
+print(f"{c:.2}")
+print(f"{c:.8}")
 
 // Complex

src/core/format_spec/string_formatter.py

@@ -87,6 +87,7 @@ class StringFormatter:
             raise PebbleRuntimeError(spec.number.decimal.dot, "Incompatible decimal options with int type.")
 
         sign: str = self.make_sign(value, spec)
+        value = abs(value)
         string: str = self.format_int_part(value, fmt_type, spec.number.integral.grouping)
 
         return sign + string