feat: add explode() annotation for OpenAPI 3.x parameters

[curiosity-the-rover]

Summary

Add support for the explode() annotation to explicitly set the explode property on query/path/header parameters in OpenAPI 3.x.

Closes #2134

Usage

// @Param ids query []string true "ID List" explode(false)
// @Param tags query []string true "Tag List" explode(true)

This allows users to control whether array/object parameters are serialized as:

• explode(true): ?ids=a&ids=b&ids=c (repeated params, default for form style)
• explode(false): ?ids=a,b,c (comma-separated)

Changes

• operation.go: Add explodeTag constant and regex pattern
• operationv3.go: Add setExplodeParamV3 function and case in switch
• operationv3_test.go: Add tests for explode(true/false/invalid)

Generated Output

parameters:
  - in: query
    name: ids
    schema:
      type: array
      items:
        type: string
    explode: false  # or true

Testing

All existing tests pass, plus new tests added for:

• explode(true) - sets explode to true
• explode(false) - sets explode to false
• explode(invalid) - returns appropriate error

Note

Important: For explode: false to be properly serialized in YAML/JSON output, the upstream dependency sv-tools/openapi needs to change Explode from bool to *bool. See: sv-tools/openapi#132

Once that PR is merged, this PR should update the dependency and change the implementation to use *bool.