Add joiner_timber truss fitting rules

[waywardmonkeys]

Introduce the no_std exedra_measurements core with exact linear and angular values. Distinguish positive Length from signed Offset, and nonnegative Angle from signed AngularOffset; retain joto iotas and microarcseconds until an explicit geometry lowering boundary.

Build the joiner_timber rule library with typed fit allowances and participant-role resolution. Model housed heels, a keyed king-post through-tenon that makes the tie tension path explicit, full-section strut bearings, and paired rafter-head bearings.

Represent every physical rule dimension and clearance as an exact Length, then lower each parameter family together when recipe construction needs meters. Keep runtime finite checks only for values derived from floating-point extents, frames, and intersections.

Derive both sides of every fit from one carried-member section, apply clearance only to receivers, reject insufficient relish and incoherent setout, and exercise every rule through deterministic constructive evaluation. Keep the keyed slot line-to-line between its load-bearing faces so the generated rectangular key realizes the contacts the construction graph claims.

Make emitted RuleOutputs read as joint contracts: name edits by their physical effect, contacts by their bearing role, generated pieces by purpose, and transfers by load direction. Retain prose where the tie-to-key-to-post suspension invariant cannot be expressed by the generic output types alone.

Record the upper strut bearing without a directed transfer because it closes the truss internal force triangle; the acyclic joiner support explanation is not a statics model. Update joiner ADR 0001 now that interacting n-ary cutters are an exedra regression contract rather than a downstream limitation.