fix: handle operators after brace initialization - #474

Fixes #373.

The brace-spacing check already recognizes several contexts where {} is initialization rather than a block, but it can misclassify a nested braced value when its closing brace is followed by an operator.

For example:

return std::optional{pmr_string{a} + " " + b};

This currently reports whitespace/braces on pmr_string{a}.

This change recognizes operator continuation after a braced value while preserving block-spacing diagnostics such as malformed requires(T t){ ... } and lambda bodies.

Regression coverage includes the original #373 shape, nested braced values followed by arithmetic, bitwise, comparison, shift, and logical operators, plus negative controls for block braces.

Validation:

• full pytest: 231 passed, 96.42% coverage
• pylint: passed
• mypy: passed
• pre-commit: passed
• git diff --check: passed