[ETFeeder] Speedup et_feeder and resolve uninitialized attrs values in ETFeederNode

[changhai0109]

1. Updated ETFeeder::readNextWindow to speed up by removing some extra resolveDeps() calls.
2. Assigned default values of attrs in ETFeederNode to avoid uninitialized variables and leading undefined behavior with -O3 compile flag.

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[srinivas212]

This is a useful fix. ET feeder is being used by other downstream use cases and we need (a) unit test (b) before and after improvements. Thanks!

[changhai0109]

Moved the commit of changing et_converter output this PR, will submit another one later.