feat(hir-def): project component EMV2 model onto instances (REQ-EMV2-PROPAGATION-002, L3/4)

[avrabe]

What

Layer 3 of 4 of the EMV2 annex→instance foundation (#294). During instantiation, the EMV2 model retained on a component's classifier (L2) is now projected onto the corresponding ComponentInstance, so Layer 4 can build the Emv2Overlay (keyed by ComponentInstanceIdx).

• SystemInstance gains a side-table emv2_models: FxHashMap<ComponentInstanceIdx, Vec<Emv2Model>> + an emv2_for(idx) accessor, mirroring the existing property_maps side-tables. Deliberately a side-table, not a ComponentInstance field — that keeps ~103 ComponentInstance constructors untouched and pays only ~56 SystemInstance literals (mostly test fixtures). (Blast-radius lesson from L2.)
• Builder::project_emv2(idx, type_loc, impl_loc) clones tree.emv2_subclauses[..].model, unioning the component's TYPE and IMPLEMENTATION subclauses (direct only), called at the two production alloc sites (main recursive path = type∪impl; type-only leaf = type only).
• Projection happens at instantiation time by necessity: Analysis::analyze receives only &SystemInstance, which has no back-reference to the item-tree — L4 can't re-read .emv2 later.
• Extends-chain EMV2 inheritance is deferred (features inherit; EMV2 intentionally does not yet — flagged in the field doc).

Verification

• Oracle-first, full pipeline (hand-authored AADL → item-tree → instantiate → assert), non-vacuous exact counts (a bare == item-tree model would only prove the clone ran): (a) EMV2 on the TYPE, root is the IMPLEMENTATION → root carries it (2 props + 1 flow), exercising the main path's type∪impl union; (b) a type-only leaf sub : device Sensor carries the device type's model (1 prop + 1 flow) while the EMV2-less root is empty — the distinct leaf alloc site a main-path-only projection would miss; (c) no annex ⇒ empty.
• Verified workspace-wide (the L2 lesson applied up-front): cargo test --workspace --all-targets --no-run 0 errors; cargo clippy --workspace 0 real warnings (the nested if let collapsed to a let-chain); spar-hir-def 467 tests pass; fmt clean; mutation on project_emv2 0-missed (2 caught, 2 unviable).
• Traceability: TEST-EMV2-INSTANCE-PROJECT verifies REQ-EMV2-PROPAGATION-002 (umbrella stays proposed until L4's end-to-end oracle).

Scope

Stops at instance projection — no Emv2Overlay, no analysis wiring. Layer 4 builds the overlay from emv2_for + wires spar analyze (the end-to-end ">0 propagation chains" oracle that closes #294 and flips the requirement to implemented).

🤖 Generated with Claude Code

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[codecov]

Codecov Report

❌ Patch coverage is 98.74214% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/spar-hir-def/src/instance.rs	98.18%	2 Missing ⚠️

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