Events should use .extend internally

[alice-i-cecile]

Should improve perf due to better memory allocation vs repeatedly pushing.

See #2145 (comment) by @NathanSWard for more details.

If you want to tackle this, either wait until #2145 is merged or work off that branch, as it changes the code organization of that file.

[NathanSWard]

I have a branch for this but will wait until #2145 either gets merged or becomes a little more stable :)

[NathanSWard]

This was fixed by #2149