There are no modifiers by robot assembly
I know there are 2 techs, 1 tradition, and 1 civic that increase assembly speed for ME.
There are also 2 traits (1 positive and 1 negative) and a relic (see patch notes) that increases assembly speed.
And for normal empires, there is the flesh is weak ascension.
Population - Stellaris Wiki
stellaris.paradoxwikis.com
I know there are 2 techs, 1 tradition, and 1 civic that increase assembly speed for ME.
There are also 2 traits (1 positive and 1 negative) and a relic (see patch notes) that increases assembly speed.
And for normal empires, there is the flesh is weak ascension.