feat(expect): support async extended matchers

[lowlighter]

This allows extended matchers in expect to return either ExtendMatchResult or Promise<ExtendMatchResult>

This changes provides additional possibilities for custom matchers, like implementing a expect(value).toBeResolved() matcher.

Example:

const { promise, resolve } = Promise.withResolvers<void>();
await expect(promise).not.toBeResolved();
resolve();
await expect(promise).toBeResolved();

// NB: this is different from expect(promise).resolves.toBe()
// Here we test the actual promise state, not its resolved value

This is just an example, but it can be used for any custom matcher that requires async operations on the right side
(for example one could image matching agains dynamically fetched files, database query results, etc.)

Side note: While this PR doesn't address specifically the following issues, the example (in the diff of the test file) shows how to implement a matcher to test promise states

• assertPromiseResolved() #3759
• suggestion: add promiseState() to @std/async #5727

Needs rebase after #6807 for lint issues

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.23%. Comparing base (08061ad) to head (34282b7).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6806   +/-   ##
=======================================
  Coverage   94.23%   94.23%           
=======================================
  Files         590      590           
  Lines       42811    42824   +13     
  Branches     6788     6793    +5     
=======================================
+ Hits        40342    40356   +14     
+ Misses       2419     2418    -1     
  Partials       50       50           

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[lowlighter]

Needs rebase after #6807 for lint issues