Fix PHP 8.4 deprecation warnings

[RocketMan]

Hello,

Deprecation warnings are being raised under PHP 8.4:

[Sat Jun 21 13:07:19.225301 2025] [proxy_fcgi:error] [pid 5242:tid 13] [client 192.168.0.103:41432] AH01071: Got error
'PHP message: PHP Deprecated: axy\sourcemap\parents\Base::__construct(): Implicitly marking parameter $data as nullable is deprecated, the explicit nullable type must be used instead in /srv/http/private/vendor/axy/sourcemap/src/parents/Base.php on line 25;
PHP message: PHP Deprecated: axy\sourcemap\parsing\FormatChecker::check(): Implicitly marking parameter $data as nullable is deprecated, the explicit nullable type must be used instead in /srv/http/private/vendor/axy/sourcemap/src/parsing/FormatChecker.php on line 23;
PHP message: PHP Deprecated: axy\sourcemap\parsing\Mappings::find(): Implicitly marking parameter $filter as nullable is deprecated, the explicit nullable type must be used instead in /srv/http/private/vendor/axy/sourcemap/src/parsing/Mappings.php on line 216;
PHP message: PHP Deprecated: axy\sourcemap\parsing\Line::__construct(): Implicitly marking parameter $positions as nullable is deprecated, the explicit nullable type must be used instead in /srv/http/private/vendor/axy/sourcemap/src/parsing/Line.php on line 21;
PHP message: PHP Deprecated: axy\sourcemap\parsing\Line::find(): Implicitly marking parameter $filter as nullable is deprecated, the explicit nullable type must be used instead in /srv/http/private/vendor/axy/sourcemap/src/parsing/Line.php on line 279'

Expected: No warnings.