fix(commoncli): prevent command prefix overreads in handleCommand

[robekl]

Summary

Fixes unsafe command-prefix parsing in CommonCLI::handleCommand that could read past the end of short input buffers.

Bug

handleCommand used fixed-length memcmp checks against command literals.
If the incoming command string was shorter than the compared length, the comparison could read beyond valid memory.

Trigger

Send a short or truncated CLI command that reaches a longer prefix check path (for example partial command tokens).

Impact

• Undefined behavior from out-of-bounds reads
• Potential crashes or hard faults on constrained targets
• Incorrect command classification from reading unrelated memory

Fix

Replaced unsafe fixed-length memcmp usage with bounded prefix matching (prefixEq) that validates string length before comparing.