fix(schema): Do not dot-expand terminal paths

[mrjones2014]

Fixes #65

Problem

When using configuration like:

{
  "yaml.schemas": {
    "./some/relative/schema.json": "relpath/*"
  }
}

The Settings.expand() function was incorrectly expanding the dots in the file path "./some/relative/schema.json", resulting in:

{
  yaml = {
    schemas = {
      ["/"] = {
        ["some/relative/schema"] = {
          json = "relpath/*"
        }
      }
    }
  }
}

Root Cause

The Settings.expand() function recursively expands all dotted keys in all nested tables. However, this is incorrect for properties like yaml.schemas which have:

• type: "object" in their JSON schema
• No properties field (indicating a free-form dictionary)

These "terminal objects" have user-defined keys (like file paths, URLs) that should NOT be treated as nested property paths.

We fix this by generating a lookup table of "terminal object" key paths at build time. Then, when dot-expanding, we stop expanding if the key path is terminal.