[astro-dev-only] Exclude with Symbol in Filename or File in Folder

Would be amazing to have some kind of symbol that can be added to the beginning of filenames to exclude them (might need an option to turn this behaviour off in case someone has a conflict with it) and similarly an empty file that could be added to folders to exclude the whole folder and its children! (Unless someone thinks excluding all child folders isn't ideal. Maybe two files that would be checked for, one that excludes all of the child folders too and one that excludes just the files from the folder in question but any child folders are still included/checked independently.)

No se nombran archivos, pruebas ni puntos de entrada. Empieza por localizar el archivo y la lógica de recorrido de carpetas del plugin astro-dev-only y, después, aclara el marcador de exclusión, el comportamiento de las carpetas hijas y la configuración de opt-out. Done debería incluir un diseño acordado y pruebas que cubran las exclusiones de nombres de archivos y carpetas.

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