Shift Decimal Place Function

People may need to format integer-based values with a decimal scale before displaying them. Given an integer and a signed shift amount, return the exact decimal representation created by moving the decimal point.

A positive places value moves the decimal point left. A negative value moves it right. The input integer is treated as a sequence of digits with an implicit decimal point immediately after the last digit. Return the result as a string so no floating-point precision is lost.

Formal Specification

Implement shift_decimal(number, places):

1. number is an integer, potentially negative, with no fractional part.
2. places is an integer. Positive values move the decimal point left, negative values move it right, and zero leaves the number unchanged.
3. Preserve all digits and any zeros required by the shift.
4. Include a decimal point only when the result has a fractional part.
5. Preserve a leading negative sign when number is negative.