Make the requirements archive to install at init

[whitphx]

One major time-taking part of the init process may be downloading and installing the packages (we must measure it first!).
So utilizing the archive-loading feature that is currently used in @stlite/desktop only may improve it.

• Bundle the necessary packages into the archive at build time and ship it with @stlite/mountable from CDN.
• CLI command to generate a single static HTML file from a bunch of source and data files #901 can bundle the user-specific packages at build time.

[Abdelgha-4]

Interesting! In most apps I've built with Stlite, installing packages definitely took +70% of the boot-up time.

I'm no expert in the underlying technology behind Stlite, but I wonder what other similar parts that could be done at build time?
I believe that currently Stlite do some work each time you open the app to mount the python source code, data etc.. (and maybe some sort of compilation? not sure). Is is possible to do all the repetitive work (from source to boot-up) in build time?

[whitphx]

This is the network profile capturing the initialization phase of Stlite Sharing.

The most time-taking part is loading the packages into the memory, rather than network access itself in my env.
The blank areas between the network accesses are it.
However anyway we can't tackle this part at this moment while it might be solved by introducing the memory snapshot by Pyodide,
and seems like optimizing the network access can also have some improvements like ~1s in my env, and more with slower networks.

Especially the last bulk of the network accesses includes many small ones which cause the long idle time as shown below, and it looks like a room for improvement in this approach.

[whitphx]

This approach can't be introduced to Stlite Sharing because the user updates the requirements and the dependencies are resolved at runtime so we can't package the initial fixed site-packages.
Contrarily, #901 can take this strategy for example as all the requirements can be resolved at packaging phase and additional requirements are never added.

[whitphx]

However, the prebuilt packages must be installed from the Pyodide distribution and their versions are fixed anyway.
So we can bundle the initially required prebuilt package wheels into a single file to avoid the HOL blocking problem, which is different from the site-packages snapshot mechanism used in the desktop package.
The desktop app doesn't have the HOL blocking problem, so the wheel files are just shipped as separate files in the app package, however, in the case of web app, there can be an advantage on bundling them into one.

Moreover, when there is no user-specified requirements, the packages loaded from PyPI is just two (blinker and tenacity) so we can ignore them and dealing with the prebuilt package wheels should have more impacts.

Because of this problem (#572, and maybe #833), the prebuilt packages can't be pre-installed in the site-packages. We should consider another way, e.g. package the wheels into a single archive, download and unpack it at runtime, and install them one by one with micropip.install().

Update: There is no HOL blocking. The CDN we are using supports HTTP/2 and HTTP/3. The green indicated "waiting the server response", not "in the queue".
For example, when the server responds each requests quickly, the network waterfall can be like this where the most length of time is occupied by downloading the resource.

[whitphx]

#1053 is an experimental PR implementing loading a single archive of the required prebuilt packages.
It is rough impl and doesn't contain some necessary parts for prod-level release such as the packaging script so we can't merge it but can see how this idea work in the deployed pages.

[whitphx]

Compare them:

• https://7f2f56a4.stlite-sharing.pages.dev/ ([DO NOT MERGE] Package the prebuilt packages required by the Streamlit and the Stlit… #1053) : finished in 6.96s
• https://99f68181.stlite-sharing.pages.dev/ (Bump pyright from 1.1.374 to 1.1.375 in /packages/kernel/py/stlite-lib #1056) : finished in 6.10s

Looks like this approach doesn't make so much improvement.

Also, the impl includes a kind of hack using Pyodide's hidden API.
We should give it up at this moment.

[whitphx]

TODO: Measure the loading performance again with Chrome's network throttle simulator.