update rustfmt.toml for projects

Summary:
At the moment these rustfmt.toml files are ignored. Our formatting tool has an explicit rustfmt.toml passed to it that overrides anything set by the code owners.

This diff updates the project's rustfmt.toml to match the one we explicitly set.

This diff also copies our explicit config in `tools/rust/ossconfigs/rustfmt.toml` to `fbsource/.rustfmt.toml`.

Reviewed By: dtolnay

Differential Revision: D84118394

fbshipit-source-id: bbc931ffd89798d5b519a1b600f11a977ac55fc8

Author: cjlongoria

rustfmt.toml

@@ -1,3 +1,9 @@
-edition = "2018"
+# Get help on options with `rustfmt --help=config`
+# Please keep these in alphabetical order.
+edition = "2021"
+format_code_in_doc_comments = true
+group_imports = "StdExternalCrate"
+imports_granularity = "Item"
 merge_derives = false
+style_edition = "2024"
 use_field_init_shorthand = true