build(rust): Fix some feature flag issues

[stinodego]

Closes #19485

[orlp]

I'm not sure that actually fixes the linked issue long-term. We should update the polars-stream toml to properly respect and propagate feature flags instead of unconditionally enabling them, especially python.

[stinodego]

I'm not sure that actually fixes the linked issue long-term. We should update the polars-stream toml to properly respect and propagate feature flags instead of unconditionally enabling them, especially python.

You're right. I tried going down the rabbit hole in #19511 but well, it's quite a rabbit hole...

This should fix the direct problem people are running into (polars-stream being compiled without explicitly requesting it) - then we can do some feature flag improvements at a later point.