[fmtappendf]

Title

docs: correct queue capacity and dial overflow semantics

Description

The queue documentation currently misstates two behaviors:

• maxDialQueueLength claims dial requests wait for capacity. New dial
  jobs actually reject with DialError when the queue is full; requests
  that join existing dial jobs are still allowed.
• onSizeLessThan claims running jobs are excluded. Its size check
  includes both waiting and running jobs.

Update both comments and supply the required limit argument in the
onSizeLessThan example. No runtime behavior changes.

Notes & open questions

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works