Fix: Ensure ModulePrinter respects the indent_char argument

[zaburo-ch]

This PR fixes a bug in ModulePrinter where the indent_char argument specified during initialization was being ignored.

Currently, the printer defaults to using a tab character (\t) for indentation, regardless of the character provided to the indent_char argument. This change ensures that the specified indent_char is correctly used when generating the output source code.

Verification

The following example demonstrates the corrected behavior.

import ast
from python_minifier.module_printer import ModulePrinter

module = ast.parse("def f():\n    while True:\n        print('hello')")

# Initialize the printer with a single space as the indent_char
printer = ModulePrinter(indent_char=" ")
result = printer(module)

# The expected output should use a space for indentation
expected = "def f():\n while True:print('hello')"

# Before this fix, the result was:
# "def f():\n\twhile True:print('hello')"

assert result == expected