fix(1270): throw descriptive error when opts.dispatcher–passed instance methods

[rozzilla]

This relates to...

Fixes #1270

Rationale

When a user passes dispatcher as an option to Pool.request(), Client.request(), or any other instance method, it is silently ignored, since the request goes through the instance the method was called on, not the provided dispatcher. This is confusing and leads to hard-to-debug behavior, especially for users behind a proxy trying to combine Pool with ProxyAgent.

Changes

• Strip dispatcher from opts via destructuring before forwarding to instance methods
• Throw InvalidArgumentError in DispatcherBase.dispatch() if opts.dispatcher is present, with a message guiding the user to either use top-level functions or call the dispatcher directly
• Add tests covering Pool.request() rejection, Client.request() rejection, and top-level request() still working with opts.dispatcher

Features

Bug Fixes

Breaking Changes and Deprecations

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.94%. Comparing base (51a27b7) to head (fe51bea).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5007   +/-   ##
=======================================
  Coverage   92.93%   92.94%           
=======================================
  Files         110      110           
  Lines       35735    35739    +4     
=======================================
+ Hits        33212    33216    +4     
  Misses       2523     2523           

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[mcollina]

lgtm

[gurgunday-spendesk]

lgtm