This changeset backports #223 from `3.x` to `1.x` to improve PHP 8.4+ support by avoiding implicitly nullable types as discussed in reactphp/promise#260. The same idea applies, but v1 requires manual type checks to support legacy PHP versions as the nullable type syntax requires PHP 7.1+ otherwise.

Builds on top of #223, #204 and #218

[1.x] Improve PHP 8.4+ support by avoiding implicitly nullable types

This ports #237 from 3.x to 1.x.

In a recent Ubuntu 24.04 runner update something changed that makes PHP
code seemingly more performant. In #236 this issue is shown to have
something to do with 24.04 because without code changes it works on 22.04. However, that doesn't fix the underlying issue.

While I'm not sure what changed, by increasing these two numbers by 10
folding them we're back at passing tests.

…t-in-excessive-tcp-query-tests

[1.x] Increase query count in excessive TCP query tests

Builds on #240 and #218 by backporting #233 to v1.

[1.x] Run tests on PHP 8.4 and update test environment

[1.x] Improve PHP 8.5+ support by avoiding deprecated `setAccessible()` calls

[1.x] Update to run tests on PHP 8.5