fix: Read method request mappings from the single annotation Spring registers (#672)

[imuromtsev]

Refs #672

Method-level request mappings were read from declared annotation values, and from every mapping annotation at once.
Spring does neither.

What Spring does

RequestMappingHandlerMapping.createRequestMappingInfo (spring-webmvc 6.2.19 :347-361, WebFlux :195-204) takes
requestMappings.get(0) and logs "Multiple @RequestMapping annotations found on …, but only the first will be used".
Probe on 6.2.19 and 7.0.9 (MVC and WebFlux gave identical results):

Method annotations	registered
bare composed @ApiGet (alias path default /items), class /api	GET /api/items
@GetMapping("/a") @PostMapping("/b")	GET /api/a only — reversed order: POST /api/b only
direct @RequestMapping("/d") + @ApiGet, both source orders	one any-verb /d; the composed GET is ignored
convention-named unaliased path	applies on 6.2.19, dropped on 7.0.9

So: one annotation wins (a direct @RequestMapping first, else the nearest composed one, ties by source order), and every
attribute — path, verbs, produces, consumes — comes from that winner. Nothing is folded in from the losers.

What changed

HandlerMethods.methodMapping(member, mah) is now the single reader: it picks the winner with
MetaAnnotationsHolder.nearestAnnotation, reads merged values, and falls back to declared PSI values when there is no UAST
element, exactly as requestMappingPrefixes does for the class level (#690). Every caller delegates to it:
SpringWebUtil.requestMappingOf and getEndpointInfo, ControllerEndpointActionsLineMarkerProvider,
EndpointRunLineMarkerProvider, RequestMappingDuplicateInspection and the MCP SpringMcpProvider.mediaTypesOf, which had the
same union defect for produces/consumes.

User-visible removal: where a method carried several mapping annotations, the Endpoints tool window and the MCP tools listed
a row per combination. They now list the one route Spring serves. A follow-up inspection ("several mappings on one element, only
the first is used") is worth filing separately.

Two smaller things in the same area:

• A declared but unreadable path (@GetMapping(SOME_UNRESOLVED_CONST)) no longer becomes a phantom row at the class prefix.
  "" now means "this mapping declares no path", which is what it meant before this PR; an unreadable one yields no row.
• The private RequestMappingVisitor in RequestMappingDuplicateInspection is deleted. It had no caller and never had one
  (git log -S over the constructor call is empty; only checkClass is overridden), so it was dead code that this PR would
  otherwise have carried forward in rewritten form.

Known gaps (unchanged by this PR, worth their own issues)

• The PSI fallback reads declared values, so a mapping source without UAST (a compiled library interface) still loses an
  @AliasFor default. This is the agreed shape of the class-level reader too.
• A verb given through a constant (method = M where val M = RequestMethod.GET) is named after the constant. Pre-existing in
  every reader.
• The gutters and getEndpointInfo still fall back to the class prefix for a declared-but-unreadable path; they did so before
  this PR as well (…mapNotNull{…}.firstOrNull() ?: "" on main).

Tests

Red first: loader/{java,kotlin}/ComposedMethodMappingTest.kt + ComposedMethodMappingFixture.kt and two cases in
inspections/{java,kotlin}/RequestMappingDuplicateInspectionTest.kt — 30 of 48 failing on the pre-fix head, with the Spring 7
classes and the use-site-alias cases green as controls. The fixtures mirror the probe sources, including both source orders.

Verification on the final head: target classes 54 tests, 0 failures; spring-web loader.* + providers.* + inspections.*
708 tests, 0 failures; spring-ai mcp.* 793 tests, 0 failures (one Exodus thread-leak flake in the batch run passed
when the class was rerun alone).

Backport

Main-only: HandlerMethods, MergedAnnotationAttributes and nearestAnnotation exist on no release/* branch.

[github-actions]

	Tests	Passed ✅	Skipped ⚠️	Failed
JUnit Test Report	4630 ran	4624 passed	6 skipped	0 failed

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