Using `include` tag errors when using `runString` without the `file` argument set

[noelforte]

Describe the bug

When compiling a template from a string using {{ include ... }}, if the file argument of runString() is left undefined, the following error is thrown:

node:internal/modules/run_main:115
    triggerUncaughtException(
    ^

NotFound [Error]: ENOENT: no such file or directory, open 'partial.vto'
    at async open (node:internal/fs/promises:639:25)
    at async readFile (node:internal/fs/promises:1246:14)
    at async Object.readTextFile (/***/tests/vento/node_modules/.pnpm/@deno+shim-deno@0.18.2/node_modules/@deno/shim-deno/dist/deno/stable/functions/readTextFile.js:12:16)
    at async FileLoader.load (file:///***/tests/vento/node_modules/.pnpm/ventojs@0.12.6/node_modules/ventojs/esm/src/loader.js:10:21)
    at async Environment.load (file:///***/tests/vento/node_modules/.pnpm/ventojs@0.12.6/node_modules/ventojs/esm/src/environment.js:86:38)
    at async Environment.run (file:///***/tests/vento/node_modules/.pnpm/ventojs@0.12.6/node_modules/ventojs/esm/src/environment.js:18:26)
    at async eval (eval at compile (file:///***/tests/vento/node_modules/.pnpm/ventojs@0.12.6/node_modules/ventojs/esm/src/environment.js:45:29), <anonymous>:11:17)
    at async Environment.runString (file:///***/tests/vento/node_modules/.pnpm/ventojs@0.12.6/node_modules/ventojs/esm/src/environment.js:32:16)
    at async file:///***/tests/vento/test.js:10:18 {
  code: 'ENOENT'
}

To Reproduce

1. Clone this reduced test case: https://github.com/noelforte/vento-runString-include-rtc
2. cd to repository
3. npm install
4. node test.js
5. See error

Expected behavior

Vento should be able to include files without needing the file argument to be set.

Desktop

• OS: macOS Sonoma 14.5
• Node version: v22.4.0 (also reproducable on Node 20)
• Vento: 0.12.8

Additional context

If the file argument has to be set for caching purposes, my use case for eleventy-plugin-vento might benefit from not having the cache to begin with (see #71).