[TASK] Update dev tools (#46)

> composer req --dev phpunit/phpunit:"^11.5.43 || ^12.4.2"
> composer req --dev friendsofphp/php-cs-fixer:^3.89.1
> composer req --dev phpstan/phpstan:^2.1.31

[TASK] Prevent PHP 8.4 deprecation (#38)

Add PHP 8.4 to test matrix. php-cs-fixer
and phpstan are not ready yet, skipped.

Update Diff->__construct() to avoid
"Implicit nullable" PHP 8.4 deprecations.

> composer req --dev phpunit/phpunit:^11.2.6

[TASK] Prevent PHP 8.4 deprecation (#38) (#39)

Add PHP 8.4 to test matrix.

Update Diff->__construct() to avoid
"Implicit nullable" PHP 8.4 deprecations.

[TASK] Require PHP mbstring (#35)

It should be fair to require true mbstring
for this package with 1.1.

> composer req ext-mbstring:*
> composer rem symfony/polyfill-mbstring

[TASK] GH workflow actions/checkout@v4 (#33)

[TASK] Raise phpstan/phpstan (#23)

Casual maintenance. Brings a huge version jump, with PHP 7.2:
composer rem --dev phpstan/phpstan
composer req --dev phpstan/phpstan

[TASK] Exclude more development files from composer packaging

[TASK] Update README.md

Version 0.3.1

Version 0.2.1