test(networkstream): randomised guard that the tree estimate never undercounts (SUB-7786)

The budget's soundness is a property over ALL inputs, not the shapes I happened to
enumerate, and process argv is arbitrary kernel bytes. 400 randomised trees built
from bytes weighted toward what JSON escapes -- <, >, &, control bytes, the short
escapes, and mostly-invalid high bytes -- each checked against real json.Marshal
output. Fixed seed, so a failure reproduces.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Alon <alon@armosec.io>