feat: add Apps endpoint and query parameter support

- add `Apps` endpoint to the `Client` struct and initialize it in
`NewClient`
- implement `doWithJsonResponse` helper to handle request execution and
JSON decoding in one step
- update `newRequest` to support passing and encoding query parameters
via `net/url`
- rename `Option` to `ClientOption` for better clarity in the
`NewClient` signature
- refactor `Ping` tests to use a more structured nested layout
- remove `option.go` and `option_test.go` as part of the configuration
refactor

clientOption.go

@@ -0,0 +1,30 @@
+package onspring
+
+import "net/http"
+
+// ClientOption is a functional option for configuring a Client.
+type ClientOption func(*Client)
+
+// WithHTTPClient sets a custom HTTP client for the Onspring client.
+// If not provided, the client will use http.DefaultClient.
+func WithHTTPClient(client *http.Client) ClientOption {
+	return func(c *Client) {
+		c.httpClient = client
+	}
+}
+
+// WithBaseURL sets a custom base URL for the Onspring API.
+// This is useful for testing or when using a different Onspring environment.
+func WithBaseURL(url string) ClientOption {
+	return func(c *Client) {
+		c.baseURL = url
+	}
+}
+
+// WithAPIVersion sets a custom API version for the Onspring client.
+// If not provided, the client will use the default API version.
+func WithAPIVersion(version string) ClientOption {
+	return func(c *Client) {
+		c.apiVersion = version
+	}
+}