fix: correct regex pattern for non-printable characters

[isatyamks]

This pull request primarily focuses on code style consistency and modernization across several vendored standard library modules. The main changes involve switching string literals from single quotes to double quotes, updating Unicode literal usage for Python 3, improving readability, and making minor formatting adjustments. These changes do not alter functionality but improve code clarity and maintainability.

String Literal and Formatting Consistency:

• Standardized string literals from single quotes to double quotes throughout metaflow/_vendor/imghdr/__init__.py and metaflow/_vendor/importlib_metadata/__init__.py, as well as in various string operations and comparisons. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

Python 3 Modernization:

• Removed unnecessary Unicode literals (e.g., u"...") and replaced them with standard string literals, as Python 3 uses Unicode strings by default. This affects control character handling and message formatting in metaflow/_vendor/click/_termui_impl.py and metaflow/_vendor/click/utils.py. [1] [2] [3]

Readability and Formatting Improvements:

• Reformatted conditional statements and function definitions for better readability, such as expanding single-line if statements and aligning argument lists. [1] [2]
• Added or adjusted blank lines for PEP8 compliance and clarity in various files. [1] [2] [3] [4]

Minor Logic and Clean-up:

• Minor logic clean-up, such as ensuring files are properly closed and removing extraneous blank lines. [1] [2] [3]

These changes collectively make the vendored codebase more maintainable and consistent with modern Python standards, without introducing behavioral changes.