Replace nette/utils and webmozart/assert with entropy

[TomasVotruba]

Slim down direct prod dependencies by reusing what the already-required entropy/entropy provides.

Changes

• Bump entropy/entropy to ^0.4.17 - this version ships Entropy\Validation\Assert
• Drop nette/utils from require:
  • Nette\Utils\Json -> Entropy\Utils\Json (decode already returns array, dropped the true arg)
  • Nette\Utils\FileSystem -> Entropy\Utils\FileSystem (dropped the trailing null mode arg)
  • Nette\Utils\Strings::match/replace -> Entropy\Utils\Regex::match/replace
• Drop webmozart/assert from require:
  • fileExists, allIsInstanceOf map directly to Entropy\Validation\Assert
  • keyExists has no entropy equivalent, replaced with an array_key_exists guard throwing ShouldNotHappenException

Direct prod requires go from 5 to 3. Both dropped packages remain available transitively via dev tooling.

Notes worth a look

• Regex::match returns [] on no match (nette returned null), so null checks became empty-array / isset guards.
• Entropy\Utils\FileSystem::write does not create parent directories (nette did), so added ensureDirectoryExists() before writing the cache file in ComposerOutdatedResponseProvider.

PHPUnit, PHPStan (level 8), ECS and Rector all pass locally.