Improve startup time by running from snapshots

[kasperl]

Did you know that you can run apps from snapshots instead of directly from source code? On the ESP32, applications written in Toit are always bundled as precompiled images, but on Linux it is possible to get some of the same benefits using snapshots.

Instead of running an example directly like this:

build/host/bin/toitvm examples/hello.toit

you can generate an intermediate snapshot and run that with the following commands:

build/host/bin/toitvm -w hello.snapshot examples/hello.toit
build/host/bin/toitvm hello.snapshot

Snapshots are faster to start from and on my machine they make running examples/hello.toit around 200 milliseconds faster; practically instantaneous!

[kasperl]

Using snapshots makes Toit run tiny scripts more than 10x faster than Python 3.

/usr/bin/time -lp build/host/bin/toitvm hello.snapshot

shows:

Hello, World!
...
             9309851  cycles elapsed
             1085440  peak memory footprint

We can compare this to Python 3.9.5's:

/usr/bin/time -lp python3 __pycache__/hello.cpython-39.opt-1.pyc 

which gives this output:

Hello, World!
...
           102023739  cycles elapsed
             4612096  peak memory footprint