chore: bump version to 1.5.3

Release 1.5.3: completes the PHP 8.4 implicit-nullable deprecation fix by
making Assets::asset()'s $version and $plugin_path explicitly nullable
(1.5.2 fixed Asset::__construct but missed Assets::asset()).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Gf8LDhhTyMZJhD6upQsFRV

Merge pull request #47 from stellarwp/fix/deprecation-notices

Fix/deprecation notices

Merge pull request #46 from stellarwp/fix/path-to-url-replacement

Fix/path to url replacement

Merge pull request #45 from stellarwp/bugfix/proper-phpstan-annotations

Assets::get() phpstan fix and add Assets::remove_all() method

Merge pull request #44 from stellarwp/fix/empty-category-enqueue

Prevents enqueueing assets when an empty array is provided

Merge pull request #43 from stellarwp/fix/hook-prefix-the-new-filter

Hook prefix the new filter

Merge pull request #42 from stellarwp/feat/allow-group-path-to-be-fil…

…tered

Allow filtering of group path

Merge pull request #38 from stellarwp/fix/dependencies-must-be-arrays

Since dependencies must be arrays, ensure they are if not a callable.

Merge pull request #39 from stellarwp/fix/return-remote-url-when-asse…

…t-is-remote

Return URL as the full path when URL was given

Merge pull request #36 from stellarwp/feat/add-full-path-api-method

Adds a full path API method