Bump to phpstan rule level 6

[paulbalandan]

Description

6. report missing typehints

Dumped errors (including the previous baseline) amounted to a whopping 613 errors!

This PR also changes the baseline from NEON to PHP format available since v1.10.2. The advantage is:

This might help with parsing performance and memory consumption in excessive baseline files that are megabytes in size. PHP code will be interpreted quicker than an equivalent .neon file.
https://phpstan.org/user-guide/baseline#php-baseline-format-instead-of-neon

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

Thanks! Nice improvements.

[kenjis]

@paulbalandan Can you also update the devkit templates?
https://github.com/codeigniter4/devkit/tree/develop/src/Template

[kenjis]

@paulbalandan How do we update the baseline?
We have now 7 errors in 4.4 branch.

The following command generates phpstan-baseline.neon:

vendor/bin/phpstan --generate-baseline

[kenjis]

I found the documentation: https://phpstan.org/user-guide/baseline#php-baseline-format-instead-of-neon