docs(actors): sync from rivet-dev/rivet

[NathanFlurry]

Automated docs sync from rivet-dev/rivet@a1c18da.

Do not edit vendor/actors/ here. Edit the docs in rivet-dev/rivet and this PR updates itself.

[the-company-company]

🟠 2 medium-severity findings

_{Reviewed commit 42769d3.}

[the-company-company]

🟠 Medium · Link metric setup to an existing section

This target has no #metrics heading, so the guide's prerequisite link lands on the environment-variable page without explaining how to expose or scrape metrics. Readers cannot complete the setup required for every PromQL example below. Link to the existing worker Prometheus setup page used by sqlite-profiling.mdx, or add the missing Metrics section before pointing here.

[the-company-company]

🟠 Medium · Document the worker-wide memory multiplier

This environment variable is read once per process, but the configured capacity is applied to each Actor's page cache. Increasing it on a worker hosting many SQLite Actors can therefore multiply memory use across all active caches, even though the surrounding experiment is framed around one Actor/query. State that tuning requires an isolated representative worker and that the production memory budget must account for concurrent Actor caches; also include the implementation's 500,000-page cap so operators know the effective range.