tasynceagain.nim flaky: Address already in use

[timotheecour]

the fix is to do something like

• fix #14320 (tasyncawait.nim is recently very flaky) + avoid hardcoding service ports everywhere + flakyAssert by timotheecour · Pull Request #14327 · nim-lang/Nim
• fix #12919 tasyncclosestall flaky: Address already in use by timotheecour · Pull Request #12934 · nim-lang/Nim

to avoid flaky Address already in use errors

CC: ci_testresults.nim
Hint:  [Link]
Hint: 56871 lines; 3.079s; 76.148MiB peakmem; Debug build; proj: /home/build/Nim/tools/ci_testresults.nim; out: /home/build/Nim/tools/ci_testresults [SuccessX]
Hint: /home/build/Nim/tools/ci_testresults  [Exec]
Category: async
Name: tests/async/tasynceagain.nim c
Action: run
Result: reExitcodesDiffer
-------- Expected -------
exitcode: 0
--------- Given  --------
exitcode: 1

Output:
tasynceagain.nim(67)     tasynceagain
asyncmacro.nim(262)      main
asyncmacro.nim(29)       mainNimAsyncContinue
tasynceagain.nim(35)     mainIter
asyncmacro.nim(262)      runServer
asyncmacro.nim(29)       runServerNimAsyncContinue
tasynceagain.nim(17)     runServerIter
asyncnet.nim(652)        bindAddr
oserr.nim(94)            raiseOSError
[[reraised from:
tasynceagain.nim(67)     tasynceagain
asyncdispatch.nim(1935)  waitFor
asyncdispatch.nim(1627)  poll
asyncdispatch.nim(1368)  runOnce
asyncdispatch.nim(208)   processPendingCallbacks
asyncfutures.nim(423)    asyncCheckCallback
]]
Error: unhandled exception: Address already in use
Async traceback:
  tasynceagain.nim(67) tasynceagain
  asyncmacro.nim(262)  main
  asyncmacro.nim(29)   mainNimAsyncContinue
    ## Resumes an async procedure
  tasynceagain.nim(35) mainIter
  asyncmacro.nim(262)  runServer
  asyncmacro.nim(29)   runServerNimAsyncContinue
    ## Resumes an async procedure
  tasynceagain.nim(17) runServerIter
  asyncnet.nim(652)    bindAddr
  oserr.nim(94)        raiseOSError
Exception message: Address already in use
Exception type: [OSError]

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