fix(configfile): fix bugs, optimize parser, add support for normal an inline comments and add unit tests (#198)

# Description

  - [ ] Feature
  - [x] Bug fix
  - [x] 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.

---------

Co-authored-by: HugoCLSC <hugo.santos.costa@gmail.com>

Author: gmmcosta15