Thirty four crates listed apsis-core or apsis-math without referencing it,
and apsis-kepler listed apsis-time and apsis-tle as well. Each was verified
removable by compiling with it taken out. An unused dependency still costs
build time and makes the dependency graph and the layer check report
relations that do not exist. The layer check now reports 104 edges, down
from 141.
README stated that a crate may only depend on layers to its left, but
nothing checked it, and the wording was self contradicting: the example
given for a cross layer jump was a reverse dependency. Clarify the rule,
add scripts/check-layers.sh to enforce it, run it in CI, and record the
boundary cases in docs/design/layers.md.
ApsisRS contributors