fix(ble): resolve BLE connection hangs on macOS without --debug flag

[lexfrei]

Summary

Fix BLE connections hanging indefinitely on macOS when not using the --debug flag.

Problem

On macOS, BLE connections would hang during scanning or connecting unless the --debug flag was specified. This made the CLI unusable for normal BLE operations without verbose output.

Root Cause

Two issues were identified:

1. Event loop race condition: The asyncio event loop thread was started, but operations could be submitted before the loop was actually running, causing deadlocks.

2. CoreBluetooth callback delivery: On macOS, CoreBluetooth requires the main thread to perform occasional I/O for callbacks to be delivered. Without --debug, no I/O occurred, so callbacks were never processed.

The --debug flag masked both issues by introducing timing delays and I/O operations through logging.

Solution

1. Added threading.Event synchronization to ensure the event loop is running before any async operations are submitted.

2. Added a sys.stdout.flush() call before waiting for async results, which triggers the necessary I/O for CoreBluetooth callback delivery.

Testing

Tested on macOS 26.2 (Tahoe):

• meshtastic --ble-scan completes successfully
• meshtastic --ble <device> --nodes connects and retrieves node information
• meshtastic --ble <device> --info works as expected

[CLAassistant]

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[CLAassistant]

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[NetBUG]

Oh, are there any people who really aren't using Meshtastic without debugging?

[codecov]

Codecov Report

❌ Patch coverage is 18.18182% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.82%. Comparing base (da559f0) to head (9b9df9e).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
meshtastic/ble_interface.py	18.18%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #893      +/-   ##
==========================================
- Coverage   59.93%   59.82%   -0.11%     
==========================================
  Files          24       24              
  Lines        4320     4329       +9     
==========================================
+ Hits         2589     2590       +1     
- Misses       1731     1739       +8     

Flag	Coverage Δ
unittests	59.82% <18.18%> (-0.11%)	⬇️

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[ianmcorvidae]

This looks reasonable to me. The stdout flush presumably isn't necessary on non-osx platforms but I don't think it'll hurt to have it there either.