Adding suffixes to duplicated sanitized param names

[kafkasl]

Problem

sanitized_params converts original spec param names to Python identifiers
(camelCase → snake_case), but doesn't check for collisions.

If an operation defines both locationCode and location_code, both sanitize to location_code, and mk_sig raises when building the Signature making the entire client unusable, not just that operation.

Real-world case: Verda Cloud's:
GET /v1/instance-availability (and
GET /v1/instance-availability/{instance_type})

define both locationCodeand location_code as query params (legacy alias).

Minimal repro

spec_json = httpx.get('https://api.verda.com/v1/openapi.json', follow_redirects=True).json()
spec = SpecParser.from_openapi(dict2obj(spec_json))
OpenAPIClient(spec)  # ValueError: duplicate parameter name 'location_code'

Fix

Make sanitized_params collision-aware. If there's a param that matches the exact original name, use that. The rest get a _ as suffix. I was considering simply dropping the duplicates because they are probably just deprecreated, but they would be unusable, happy to change that or listen to other solutions @KeremTurgutlu

• Params whose sanitized name equals their original name claim it first
  (location_code keeps location_code).
• Renamed params append _ on collision (locationCode → location_code_).

Only the Python-side identifier changes; the original name is still sent
on the wire (same mechanism as the existing keyword handling, e.g. class_).
Non-colliding specs are unaffected.