chore: add Rector rules for setter refactorings

[gharlan]

Summary

Adds two custom Rector rules that are useful for the in-progress 5→6 upgrade set and for future refactorings:

• MethodCallToPropertyAssignRector — turns stand-alone setter statements $obj->setX($v); into $obj->x = $v;. Only statement-form calls are touched, so fluent setters returning $this and setter calls embedded in other expressions stay intact.
• SetterCallToConstructorArgumentRector — merges a setter call directly following a new assignment into a named constructor argument (new Foo(...); $foo->setX($v); → new Foo(..., x: $v);). Conditional or non-adjacent setters are left for manual cleanup.

Configures MethodCallToPropertyAssignRector for the existing ArticleSliceAction::setSave conversion (resolving the // todo setter marker in rector.php). SetterCallToConstructorArgumentRector ships unconfigured here — it will be wired up in the follow-up API-functions PR.

[Copilot]

Pull request overview

Adds two custom Rector rules to support the ongoing 5→6 upgrade refactorings, and wires one of them into the project’s rector.php config to automate a specific setter-to-property migration.

Changes:

• Add MethodCallToPropertyAssignRector (+ value object) to convert stand-alone setter statements into property assignments.
• Add SetterCallToConstructorArgumentRector (+ value object) to merge adjacent setter calls into named constructor arguments (rule included but not yet configured).
• Configure MethodCallToPropertyAssignRector in rector.php for ArticleSliceAction::setSave → $action->save = ... conversion.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rector.php	Imports the new value object and configures MethodCallToPropertyAssignRector for ArticleSliceAction::setSave.
.tools/rector/ValueObject/SetterCallToConstructorArgument.php	Adds configuration value object for the constructor-argument merge rule.
.tools/rector/ValueObject/MethodCallToPropertyAssign.php	Adds configuration value object for the setter-to-property-assign rule.
.tools/rector/Rule/SetterCallToConstructorArgumentRector.php	Implements configurable Rector rule to merge adjacent setter calls into named constructor args.
.tools/rector/Rule/MethodCallToPropertyAssignRector.php	Implements configurable Rector rule to replace setter statements with property assignments.

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