RequestConfig.Execute corrupts base URL path tail.

[iamwavecut]

How to reproduce an isolated problem: https://go.dev/play/p/I0RUm0AIx_2

package main

import (
	"log"
	"net/url"
	"strings"
)

func main() {
	baseURLString := "http://base.url/some/path/v1"
	cfgRequestPath := "chat/completions"
	expectedURLString := "http://base.url/some/path/v1/chat/completions"

	baseURL, err := url.Parse(baseURLString)
	if err != nil {
		log.Fatal(err)
	}

	resultURL, err := baseURL.Parse(strings.TrimLeft(cfgRequestPath, "/"))
	if err != nil {
		log.Fatal(err)
	}

	log.Println("result URL == expected URL", resultURL.String() == expectedURLString)
	log.Println("expected URL", expectedURLString)
	log.Println("result URL", resultURL.String())
}

Actual result:

result URL == expected URL false
expected URL http://base.url/some/path/v1/chat/completions
result URL http://base.url/some/path/chat/completions

The URL construction logic is flawed, as it overwrites the last part of the BaseURL if it lacks a trailing slash.

Suggested fix:

Ensure that the BaseURL consistently ends with a trailing slash to prevent accidental truncation during path joining.