fix(hir-def): applies_to accepts feature paths per AADL v2.3 (v0.9.x bug closeout)

[avrabe]

Summary

AADL v2.3 (SAE AS5506D §11.3) permits a contained property association's applies to clause to end with a feature name. spar previously walked the dotted path matching only subcomponents, so when the final segment named a feature it emitted a spurious "could not be resolved" diagnostic and dropped the property.

MWE

system implementation Sys.Impl
  subcomponents
    cpu: processor Cpu;
    fw: process Proc.Impl;          -- contains thread `w` with feature `input_port`
  properties
    Required_Connection_Quality_Of_Service => (Latency)
      applies to fw.w.input_port;   -- pre-fix: diagnostic + dropped
end Sys.Impl;

What changed

crates/spar-hir-def/src/instance.rs:

• New enum AppliesTarget { Component, FeatureOwner, Unresolvable }.
• resolve_applies_to_path: each non-final segment must name a subcomponent (as before); the final segment may name either a subcomponent or a feature on the resolved component. When it names a feature, the property attaches to the component that owns the feature.
• Unresolvable paths still emit the existing diagnostic, now with text "could not be resolved to a component instance or feature".

Test plan

• applies_to_feature_path_does_not_emit_unresolved_diagnostic — clean resolution of fw.w (subcomponent) and fw.w.input_port (feature)
• applies_to_unknown_segment_still_emits_diagnostic — fw.w.no_such_port still emits the unresolved diagnostic
• cargo clippy -p spar-hir-def -p spar -- -D warnings clean
• Existing applies_to_nested.rs + applies_to_unresolvable_path_emits_diagnostic tests still pass

Part of v0.9.x bug closeout series (#214 nested binding, #216 classifier_match, #217 has-features, #218 count-comparisons).

Co-Authored-By: Claude Opus 4.7 noreply@anthropic.com