fix(issue #3279): More traceback cleaning

[arunsoman]

Fixes #3279

What

autonomous fix via atomic-forge fix — CIE (code graph over MCP) localized the bug, generated a failing regression test, and forge's repair loop fixed the source against it.

Issue

More traceback cleaning

https://vorpus.org/blog/beautiful-tracebacks-in-trio-v070/ made tracebacks in some scenarios nicer, but afaict it mostly just affects calls to trio.run and when spawning tasks. (Implementation. Tested in test_traceback_frame_removal).

But there's still a lot of other scenarios that cause verbose outputs:

import trio
import trio.testing

cl = trio.CapacityLimiter(1)
async def borrower() -> None:
    await cl.acquire()
    await trio.sleep_forever()

async def main() -> None:
    async with trio.open_nursery() as nursery:
        nursery.start_soon(borrower)
        await trio.testing.wait_all_tasks_blocked()

        with trio.fail_after(1):
            async with cl:
                pass
trio.run(main)

  + Exception Group Traceback (most recent call last):
  |   File "/home/h/Git/trio/clean_tb/test_foo.py", line 16, in <module>
  |     trio.run(main)
  |     ~~~~~~~~^^^^^^
  |   File "/home/h/Git/trio/clean_tb/src/trio/_core/_run.py", line 2529, in run
  |     raise runner.main_task_outcome.error
  |   File "/home/h/Git/trio/clean_tb/test_foo.py", line 10, in main
  |     async with trio.open_nursery() as nursery:
  |                ~~~~~~~~~~~~~~~~~^^
  |   File "/home/h/Git/trio/clean_tb/src/trio/_core/_run.py", line 1122, in __aexit__
  |     raise combined_error_from_nursery
  | ExceptionGroup: Exceptions from Trio nursery (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
    |   File "/home/h/Git/trio/clean_tb/src/trio/_sync.py", line 342, in acquire_on_behalf_of
    |     self.acquire_on_behalf_of_nowait(borrower)
    |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
    |   File "/home/h/Git/trio/clean_tb/src/trio/_sync.py", line 312, in acquire_on

## How it was verified
- regression test: `tests/test_forge_3279.py` (CIE-generated; fails on the pre-fix code, passes on the fix)
- repair rounds: 2  failures: 1 -> 0
- repaired file(s): src/trio/_core/_run.py

---
<!-- atomic-forge:pr -->
[![Fixed by Forge](https://img.shields.io/badge/fixed_by-atomic--forge-6f42c1?logo=github)](https://github.com/kannamma-labs/atomic-forge)

🔨 Fixed by [Forge](https://github.com/kannamma-labs/atomic-forge) — an autonomous, test-driven issue→PR repair engine (`atomic-forge fix <issue-url>`).

⭐ If you found this useful, a star on [atomic-forge](https://github.com/kannamma-labs/atomic-forge) helps other maintainers find the tool that fixed your bug.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 99.99486%. Comparing base (d5eb534) to head (e863d33).

Files with missing lines	Patch %	Lines
src/trio/_core/_run.py	50.00000%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##                 main       #3498         +/-   ##
====================================================
- Coverage   100.00000%   99.99486%   -0.00514%     
====================================================
  Files             128         128                 
  Lines           19452       19454          +2     
  Branches         1321        1322          +1     
====================================================
+ Hits            19452       19453          +1     
- Partials            0           1          +1     

Files with missing lines	Coverage Δ
src/trio/_core/_run.py	99.90530% <50.00000%> (-0.09471%)	⬇️

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