Description

• Feature
• Bug fix
• Code refactor
• Documentation

This pull request introduces:
- Fix data-corruption bug in _parse_file: separator normalisation was replacing every : and = in a line instead of just the first one, silently mangling URLs, tokens, and section
names with colons
- Fix get(), getint(), getfloat(), getboolean() default-handling: missing options with no default now raise NoOptionError instead of returning Sentinel.MISSING; get() no
longer passes the fallback through the parser
- Fix add_option(value=None) writing the literal string "None" instead of a value-less option line
- Convert all logger calls to %-style, add exc_info=True and file path to save_configuration error, add exception chaining (from e) throughout
- Ignore regular and inline comments in configfile
- Enforce singleton pattern in get_configparser(): only one BlocksScreenConfig and one ConfigParser instance exists for the application lifetime, using double-checked locking; add
reset_configparser() for test isolation
- Enforce : as the sole stored separator: _RE_SEP_NORMALIZE accepts both = and : from disk and normalises to : ; all downstream code (_RE_OPTION, _find_option_line_index,
ConfigParser(delimiters=...)) restricted to : only
- Remove unused check_file_on_path import; replace with Path.exists() on module-level path constants
- Add 80 unit tests covering all of the above plus thread safety, view sharing, and factory behaviour

Motivation

The configfile module had several subtle parsing bugs and inconsistent behaviors that could corrupt configuration values (e.g., URLs, tokens, or section names) and return incorrect
results in some edge cases.

This PR stabilizes the module by fixing multiple correctness issues, tightening error handling, and improving logging. The singleton refactor ensures all consumers share one parsed state so
that update_option/save_configuration mutations are immediately visible everywhere without a reload. The separator enforcement removes misleading redundancy — = is accepted on read
but normalised before storage, so no downstream code needs to handle it.

To prevent regressions and make future changes safer, a comprehensive unit test suite (80 tests) was added, covering parsing behaviour, comment handling, deduplication, all read methods,
view sharing, add/update/save lifecycle, factory and singleton behaviour, RLock reentrancy, and thread safety.

Tests

tests/util/test_configfile_unit.py: 80 unit tests. Covers parsing, comment handling, deduplication, all read methods, get_section view sharing, add/update/save lifecycle,
get_configparser singleton factory, reset_configparser, RLock reentrancy, thread safety, and stale-view-after-reload.