Drain protocol ema when net_flow disabled

[gztensor]

Description

While net_flow_enabled is disabled, protocol flow accumulates indefinitely without EMA updates, causing a massive one-time emission distribution shock across subnets when the flag is re-enabled.

Related Issue(s)

• Closes NetTaoFlowEnabled toggle injects accumulated SubnetProtocolFlow into the EMA as a single block #2667

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run ./scripts/fix_rust.sh to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules