fix: prevent SSHTransport busy-loop on partial packets

[vicajilau]

Fixes #177.

SSHTransport._scheduleProcessData busy-loops at 100% CPU whenever a partial packet is left in the read buffer, permanently starving the event loop (and the socket reads that would complete the packet). On Flutter this pegs the platform thread and produces an "Input dispatching timed out" ANR / frozen UI.

Root Cause

_processPackets returns as soon as _consumePacket() cannot form a complete packet. But whenComplete reschedules whenever _buffer.isNotEmpty, even when the pass consumed nothing. The reschedule runs as a microtask; microtasks have priority over I/O events, so the loop starves _onSocketData — the additional bytes needed to complete the packet are never delivered, and it spins forever.

Fix

Only reschedule when the pass actually made progress (a packet was consumed) or new bytes arrived while processing (tracked by a new _hasNewData flag).

Also added a unit test to verify that the event loop is not starved when receiving a partial packet.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 54.85%. Comparing base (1d3ed4a) to head (b53960a).

Files with missing lines	Patch %	Lines
lib/src/ssh_transport.dart	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #179      +/-   ##
==========================================
+ Coverage   54.67%   54.85%   +0.18%     
==========================================
  Files          66       66              
  Lines        5419     5423       +4     
==========================================
+ Hits         2963     2975      +12     
+ Misses       2456     2448       -8     

Flag	Coverage Δ
unittests	54.85% <80.00%> (+0.18%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
lib/src/ssh_transport.dart	52.58% <80.00%> (+1.66%)	⬆️

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