feature: Add IsReadonly Expression

[helyakin]

Hey there !

First of all I wanted to say how cool I find this package. It is very useful so thank you everyone !

I've started coding before reading the guidelines so maybe this will directly be closed.
Hopefully not 🙏🏻

So I'm with my project where I would like to enforce the classes to be readonly in a directory
And since I know using the reflection you directly have access to this value, so I figured it would not be that a big of a deal 🧠

I figured it should look like something like that:

$rules[] = Rule::allClasses()
        ->that(new ResideInOneOfTheseNamespaces('App\Domain\Event'))
        ->should(new IsReadonly())
        ->because('All event have to be readonly.')
    ;

I guess I should wait for your input before continuing in this way ?

Do you think this would be helpful for the community ?

Thank you for your time in any case and have a nice day !

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (e29c207) 94.35% compared to head (f16c7f9) 94.19%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/Analyzer/ClassDescriptionBuilder.php	40.00%	3 Missing ⚠️
src/Analyzer/FileVisitor.php	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##               main     #422      +/-   ##
============================================
- Coverage     94.35%   94.19%   -0.16%     
- Complexity      573      582       +9     
============================================
  Files            67       69       +2     
  Lines          1505     1533      +28     
============================================
+ Hits           1420     1444      +24     
- Misses           85       89       +4     

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[fain182]

Thank you for your contribution @helyakin !
I think this looks very good 🙂
If you could add the negative rule IsNotReadOnly, and a couple of lines in the README to show an example (like the other rules) and then we are ready for merging it!

[helyakin]

Thanks for your quick review @fain182

I'm super thrilled that you find this contribution interesting and worth adding 🙏🏻

I've just added the requested changes.

[fain182]

great work, thanks!