feat: add ExtraParams support for declaring path params not in input models

[c-wygoda]

Summary

• Add ExtraParams field to OperationInfo for declaring additional path/query parameters
• Add ExtraParam struct for parameter metadata
• Add PathParam() and QueryParam() OperationOption functions
• Update generator to include extra params before OpenAPI path param validation

Background

This enables declaring path parameters at the operation level when they come from parent routes (e.g., /v1/:contract_id/...) and are not defined in handler input models.

Without this, fizz's OpenAPI validation fails with:

declared path parameter contract_id needs to be defined at operation level

Usage

r.GET("/v1/:contract_id/items", []fizz.OperationOption{
    fizz.PathParam("contract_id", "The contract identifier"),
    fizz.Summary("Get items"),
}, handler)

Test plan

• Verify fizz compiles
• Test integration with stacster path param support

🤖 Generated with Claude Code

[c-wygoda]

Closing this PR - we found a workaround by embedding BasePathParams in input structs, which allows fizz to find path params via reflection without requiring library changes. This enables releasing stacster as OSS without needing to merge fizz changes first.