feat: treat experimental apiKind identically to no-BWC in compatibility scope

[makeev-pavel]

Summary

Treat x-api-kind: experimental identically to x-api-kind: no-BWC when classifying API changes. Operations and channels marked as experimental now produce risky (instead of breaking) changes in both REST and AsyncAPI compatibility scopes.

Changes

Source code (3 files, ~30 lines):

• src/consts.ts — added isNoBwcOrExperimental helper
• src/components/compare/rest.bwc.validation.ts — replaced direct === NO_BWC checks with isNoBwcOrExperimental(), added predicate-based checkAllMethodsMatchApiKind to handle mixed apiKind within a single pathItem (e.g. GET=no-BWC, POST=experimental)
• src/components/compare/async.bwc.validation.ts — updated toApiCompatibilityKind to treat experimental the same as no-BWC

Tests (3 files, +133 tests):

• test/apiKinds.test.ts — experimental-only (labels, info, operation, remove), mixed no-BWC/experimental, mixed apiKind within pathItem
• test/asyncapi-build-apikind.test.ts — calculateAsyncApiKind unit tests for experimental and mixed
• test/asyncapi-changelog-apikind.test.ts — full experimental coverage across all scopes (root, channel, operation), all change types (remove operation/channel/message, modify payload)

Fixtures (22 YAML files):

• 12 experimental-only fixtures (info/operation/remove levels)
• 8 mixed no-BWC↔experimental fixtures
• 2 mixed apiKind within same pathItem fixture