$geoNear key auto-inference; CI ccache passthrough shim
v0.3.0a29 polishes the geo aggregation stage: $geoNear no longer requires an explicit key: argument when the target collection has exactly one geo index — the field is inferred automatically. This brings parity with mongod's behaviour and removes a footgun from the embedded-server use case.
CI also gets a passthrough shim: when apt-get install ccache fails on a particular image, builds now fall back to a no-op ccache wrapper instead of erroring out, so a transient apt mirror flake can't break the publish workflow.