Small non-breaking improvements

[Matthiee]

This PR applies some small left over improvements:

• Remove deprecated library name
• Fix dynamic type usage
• Fix comments
• Fix import statement
• Improve read without mutations

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (0b5103b) to head (c53a857).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #35   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines          519       518    -1     
=========================================
- Hits           519       518    -1     

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[Copilot]

Pull request overview

This PR applies a set of small internal cleanups across the mediator/request/event layers, focusing on removing deprecated references, tightening generic typing, and preventing read operations from mutating internal stores.

Changes:

• Tighten generic typing in request pipeline execution and fix an internal import to avoid deprecated/incorrect library usage.
• Adjust event handler store reads to avoid mutating internal state during lookups.
• Minor comment/doc cleanup and removal of named library directives in public entrypoints.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
lib/src/request/request_manager.dart	Strengthens typing for the composed pipeline execution delegate.
lib/src/request/pipeline/pipeline_configurator.dart	Replaces deprecated/incorrect import with direct type imports needed by the configurator API.
lib/src/event/subscription_builder/distinct_builder.dart	Updates comment to match distinct operator behavior (first event is emitted).
lib/src/event/handler/event_handler_store.dart	Makes handler lookups non-mutating by avoiding putIfAbsent on read paths.
lib/request_manager.dart	Removes named library directive (now uses empty library;).
lib/reactive.dart	Removes named library directive (now uses empty library;).
lib/mediator.dart	Converts header comment to doc comment and removes named library directive (now uses empty library;).
lib/event_manager.dart	Removes named library directive (now uses empty library;).
lib/contracts.dart	Removes named library directive (now uses empty library;).

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