The knob tested `v == "0"` for the disable case and treated everything else that was set as
a force-enable. So a trailing space — the kind a `.env` line or a shell script leaves behind
— made `PUNKTFUNK_VULKAN_RGB_DIRECT=0 ` mean the exact opposite of what the operator wrote,
forcing the RGB-direct encode source on. On a cursor-blend session that is not a subtle
difference: the EFC front-end cannot blend, so the pointer disappears from the stream. An
empty value and any typo did the same thing.
Now parsed like every sibling knob in the crate — `matches!(v.trim(), "1"|"true"|"yes"|"on")`
and the matching false spellings — so unrecognised input falls back to the default instead
of being read as a force-on. `=0` and `=1` keep working exactly as documented.
Splits the parse into a pure function so the accepted spellings are covered by tests. That
matters more than it looks: the env-var read itself is untestable in a parallel test binary
(the process environment is shared), which is precisely why this knob's behaviour had no
coverage and the inverted case survived.
Verified with the canonical Linux gate (docker linux/amd64): fmt, clippy --all-targets at
default and at nvenc,vulkan-encode,pyrowave, and the pf-encode test leg (37 passed).
enricobuehler
ed525c4c73