fix(lib-std-fs): handle usize overflow in read_to_string

[Rudxain]

I assume this is a non-breaking change, as there would be an OOM panic anyways. This patch ensures a fast-fail when there's not enough memory to load the file. This only changes behavior on platforms where usize is smaller than 64bits

[rustbot]

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[rust-log-analyzer]

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

##[endgroup]
[TIMING] core::build_steps::tool::ToolBuild { compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu, tool: "tidy", path: "src/tools/tidy", mode: ToolBootstrap, source_type: InTree, extra_features: [], allow_features: "", cargo_args: [], artifact_kind: Binary } -- 9.130
[TIMING] core::build_steps::tool::Tidy { compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu } -- 0.000
fmt check
Diff in /checkout/library/std/src/fs.rs:346:
 pub fn read_to_string<P: AsRef<Path>>(path: P) -> io::Result<String> {
     fn inner(path: &Path) -> io::Result<String> {
         let mut file = File::open(path)?;
-        let size = file
-            .metadata()
-            .map(|m| usize::try_from(m.len()).unwrap_or(usize::MAX))
-            .ok();
+        let size = file.metadata().map(|m| usize::try_from(m.len()).unwrap_or(usize::MAX)).ok();
         let mut string = String::new();
         string.try_reserve_exact(size.unwrap_or(0))?;
         io::default_read_to_string(&mut file, &mut string, size)?;
fmt: checked 6143 files
Build completed unsuccessfully in 0:00:44
  local time: Fri Jul  4 23:22:05 UTC 2025
  network time: Fri, 04 Jul 2025 23:22:05 GMT
##[error]Process completed with exit code 1.

[a1phyr]

Shouldn't this fail with ErrorKind::OutOfMemory directly instead?

Also modifications to fs::read_to_string should be made to fs::read too, as they are essentially the the function.