Faster website build - #3660

Theme explanations dominate highlighting time but are only consumed by
TSConfig's JSON property hovers. Keep those scopes without computing
unused explanations for every other language, and reuse tokenization
for repeated examples without sharing mutable tokens.

All 920 localized page-data files remain identical. Rendered HTML is
unchanged apart from existing random links and build identifiers.

Several package bootstrap scripts are aliases for their build, which
runs again at the end of workspace bootstrapping. TSConfig generation
also repeats work already done by its build. Do the metadata setup and
one topologically ordered build instead, preserving the package-level
bootstrap commands for direct use.

Compiled package outputs are unchanged.

Reusing compiled examples across builds must not confuse identical code
in different languages or with different compiler settings. Include
those inputs and the VFS version before enabling persistent CI reuse.

Production Gatsby builds spend most of their time compiling examples
and recreating Webpack bundles. Reuse that work across compatible
builds without restoring Gatsby's page-query cache or generated pages.
Keep translations, metadata, and playground cache busting fresh.

A fully localized local site build took 253 seconds without caches and
31 seconds restoring only Twoslash and Webpack work, including the
production cache-busting step. All 920 page queries still run.

Separate build steps also make future Actions bottlenecks visible.

Restored snapshots carry obsolete examples forward indefinitely unless
entries are explicitly evicted. Record usage on successful cache reads
and prune the least-recently-used entries to a 64 MiB budget before
saving, preserving usage timestamps across archive roundtrips.

GitHub cache archives are immutable, so repeated builds of the same
commit cannot otherwise save newly compiled examples or refreshed
usage order. Restore the latest compatible snapshot and save a pruned
replacement under a unique run-and-attempt key as soon as the site
build succeeds, even if subsequent tests or deployment fail.

Playground changes should not force unchanged documentation examples
to compile again. Hashing workspace sources, including generated
inputs, makes those iterations cold.

Broader snapshot reuse requires example-level checks of compiler
implementations and filesystem dependencies. Package versions alone
cannot detect rebuilt workspace compilers or changed declarations,
and missed module lookups must be reconsidered when new files appear.

Regenerating the same reference after the CLI documentation adds eight
seconds to package preparation on CI without changing its output.

CI already builds every package before building the site. Repeating the
generators during tests adds 42-54 seconds without providing another check.

Keep standalone tests unchanged. Validate generated documentation before
running independent package tests with bounded concurrency, avoiding the
unrelated dependency barriers in the test phase.

Documentation linting compiles examples with different settings from the
site build. Saving only before tests discards that work, costing 65-76
seconds on each CI run.

Save a second bounded snapshot after successful tests with a distinct
immutable key. Keep the earlier checkpoint so failed tests still preserve
the completed site build.

The website and package tests do not need to share a runner or wait for
each other. Run both operating-system matrices independently so package
validation no longer extends the site build critical path.

Keep Gatsby-dependent checks and documentation validation with the site,
retain every required check, and preserve the CI workflow and site artifact
consumed by preview deployment. No additional interbuild caches are needed.