[Feature] Resolve positional @feature.index and bare xmi:id URI fragments (#106)

[samatstariongroup]

What

Closes #106. Adds the two EMF URI-fragment-resolution forms that Resource.GetEObject did not previously support:

1. Positional @feature.index fragments — e.g. #//@eClassifiers.3/@eStructuralFeatures.1. Resolved by structural navigation from the resource root, indexing into the containment feature named by each segment (mirrors EMF's eObjectForURIFragmentSegment). Works same-file and cross-file.
2. Bare xmi:id fragments — a fragment without a leading slash (e.g. #_node), which EMF resolves via getEObjectByID. Any element carrying an xmi:id is now recorded in a per-resource id→object map during ReadXml, and consulted when the fragment is not a /-rooted path.

(The name-based name.N disambiguation form already resolved since #96, since the disambiguated identifier is the cache key.)

How

• EObject.ReadXml now calls a small RegisterXmiId() after saving attributes: if the element has an xmi:id, it registers itself with the resource. Covers named and unnamed (EGenericType) objects alike.
• Resource gains an idToEObject map + RegisterEObjectId (first-writer-wins; a duplicate xmi:id is invalid but must not abort the load).
• Resource.GetEObject tail is restructured: after the cache and built-in-type lookups miss, it computes the in-document fragment and delegates to a new ResolveInDocumentFragment:
  • /-rooted and contains @ → ResolveStructuralFragment (positional navigation).
  • /-rooted, no @ → returns null (pure name paths are already covered by the identifier cache).
  • otherwise → xmi:id lookup.
    This runs for the owning resource, which is this resource for a same-file positional reference (rewritten to file.ecore#//@…) and a sibling for cross-file references. It is evaluated before the cross-resource delegation, so it never trips the cycle guard.
• Structural navigation maps each @feature name to the owning object's containment list (eClassifiers, eSubpackages, eStructuralFeatures, eOperations, eGenericSuperTypes, eLiterals, eParameters, eGenericExceptions, eTypeParameters, eBounds, eAnnotations) and indexes into it.

No existing behaviour changes: name-based and file-delegated resolution paths are unchanged; the new paths only fire on fragments that previously returned null.

Tests

New ECoreNetto.Tests/Resource/PositionalAndIdFragmentTestFixture.cs (6 tests, synthetic models):

• same-file positional eType references;
• a deep positional path resolving to a structural feature via GetEObject;
• a comprehensive test navigating every supported containment feature;
• same-file xmi:id (including the duplicate-id first-wins case);
• cross-file positional and xmi:id;
• negatives: out-of-range index, unknown/missing feature, non-@ segment, @feature without index, non-numeric index, missing name path, empty fragment, unknown xmi:id.

Full solution builds with 0 warnings; entire suite green (281 tests, +6).

Scope

Splits from #106 as agreed; EAnnotation.contents (needs a dynamic EObject) remains tracked separately in #109.

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
ECoreNetto	91%	87%	690	✔
ECoreNetto.Extensions	99%	92%	101	✔
ECoreNetto.HandleBars	99%	97%	60	✔
ECoreNetto.Reporting	83%	71%	181	✔
ECoreNetto.Tools	95%	92%	58	✔
Summary	91% (2590 / 2835)	85% (741 / 870)	1090	✔

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
95.5% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud