[kotlin-spring] add @ModelAttribute to complex non-json query params

[Picazsoo]

This PR fixes kotlin-spring generator to correctly annotate complex query parameters (isModel=true) with @ModelAttribute("paramName"). Previously, model query params received no Spring binding annotation at all, which meant Spring couldn't reliably bind nested fields like filter.statuses=active in Kotlin where parameter names aren't discoverable without -java-parameters compile flag. Additionally, query params with hyphenated names (e.g. order-status, item-status) that can't be Kotlin identifiers had no way to be bound at all without the explicit annotation value.

A guard was added for the content: application/json case so when the parameter carries a JSON-encoded object as a single string on the parameter (e.g. ?filter={"statuses":["active"]}), @ModelAttribute would be wrong - Spring's data binder would try to read filter.statuses=… style fields rather than deserializing the JSON blob. These params instead properly get @RequestParam annotation, which delivers the raw string to a (user provided and registered) Converter<String, T>.

Tests:

• The runtime behaviour is verified in the kotlin-springboot-sort-validation sample: OrdersApiImpl uses check() assertions with distinct sentinel values per parameter, so any mis-routing (e.g. order-status.statuses landing in filter) or missing binding (e.g. a hyphenated name not bound at all) returns immediately as HTTP 500.
• Unit-level coverage lives in KotlinSpringServerCodegenTest with three targeted tests covering deepObject model params, non-Kotlin-identifier param names, and the content: application/json exclusion.

Note: I will eventually implement the same in java-spring as well.

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Summary by cubic

Adds @ModelAttribute("") for complex (model) query parameters in kotlin-spring to enable deepObject binding and preserve wire names, while keeping @RequestParam for JSON-encoded (content: application/json) query params. Updates samples and tests to verify correct binding, including hyphenated names, multiple model params, and valid-identifier params.

• New Features
  • Generate conditional annotations for model query params: use @ModelAttribute("<baseName>") for deepObject/form-style; use @RequestParam when the param uses content: application/json.
  • Update Kotlin and Java Spring Boot samples: add Orders endpoints and OrderStatus schema, a Kotlin OrdersApi implementation with runtime assertions, a Java controller, and tests (MockMvc + codegen) covering hyphenated names, multiple model params, valid-identifier params, and the JSON-content exclusion.

^{Written for commit 2634014. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}

[cubic-dev-ai]

No issues found across 8 files

_{Re-trigger cubic}

[Picazsoo]

This implementation is mostly nonsense and was based on incorrect understanding of the matters. Closing the PR.