feat(go): Dynamic snippets support exportedClientName

[amckinney]

This updates Go's dynamic snippet generator to respect the exportedClientName configuration. With this, the generated snippet references the correct constructor method like so:

# generators.yml
- name: fern-api/fern-go-sdk
  version: 0.33.0
  config:
    exportedClientName: FernClient

client := client.NewFernClient(
    option.WithToken(
        "<YOUR_API_KEY>",
    ),
)

Note that this also refactors the DynamicSnippetsGenerator and DRYs up a few things with the new EndpointSnippetGenerator and Result classes.