refactor(next): streamline AST execution bridges and eliminate query adapter layers (#576)

[remiceres]

Summary

Streamlines and simplifies the execution bridge layers in fr.inria.corese.core.next.query.impl.sparql.bridge to eliminate unnecessary intermediate translation wrappers between the Next SPARQL AST and the query execution pipeline.

Closes #576

Changes

• Centralize term resolution: Moved term-to-node resolution directly into SparqlTermResolver.toNode(TermAst), eliminating duplicated switch logic across bridge classes.
• Eliminate builder indirection: Replaced static indirections in CoreseAstQueryBuilder and NativeEvaluationContext with direct calls to termResolver.toNode(term).
• Relocate path predicate extraction: Moved simplePredicate(PathAst) to WhereCompiler where query and construct graph patterns are resolved.
• Clean up imports & formatting: Removed redundant explicit imports and normalized EOF newlines across bridge classes.
• Unit testing: Added dedicated unit tests in AstBackedExprTest covering AST term resolution, literal parsing, filter views, variable bindings, and immutability contracts.

Verification

• ./gradlew compileJava compileTestJava: SUCCESS (0 errors, 0 warnings).
• ./gradlew test: 2,628 tests executed, 2,628 passed, 0 failures.
• ./gradlew enforceW3cRegressions: 2,327 stable passes, 0 regressions, 141 tests transitioned to passed.
• SonarLint LSP scan: 0 alerts across all modified files.

[github-actions]

Overall Project	52.93% -0.01%	🍏
Files changed	88.54%	🍏

File	Coverage
WhereCompiler.java	97.89% -2.11%	🍏
CoreseAstQueryBuilder.java	92.72%	🍏
NextFilterFromAst.java	80.95%	🍏
SparqlTermResolver.java	66.32% -2.89%	🍏
NativeEvaluationContext.java	64.81%	🍏
AstBackedExpr.java	54.84%	🍏

[github-actions]

Test Results

  425 files    425 suites   25s ⏱️
2 639 tests 2 639 ✅ 0 💤 0 ❌
2 653 runs  2 653 ✅ 0 💤 0 ❌

Results for commit 1af1045.