Add compatibility with Spiral Framework 3.12.0 dispatchers

[msmakouz]

What was changed

1. Since version 3.12, the dispatchers property in Kernel will contain an array of class-strings, not objects. For compatibility with both variants, the ability to work correctly with both strings and objects has been added.
2. Method canServe will be removed from the interface and a static method 'canServe' accepting 'Spiral\Boot\EnvironmentInterface' in parameters will be added to all dispatchers. The static method will be added to the interface in version 4.0. The package code should be able to work with both method variants.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (03808a8) 43.19% compared to head (912871b) 44.57%.

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x      #70      +/-   ##
============================================
+ Coverage     43.19%   44.57%   +1.37%     
- Complexity      330      332       +2     
============================================
  Files            34       34              
  Lines          1139     1142       +3     
============================================
+ Hits            492      509      +17     
+ Misses          647      633      -14     

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