[Breaking] Remove ResumableFileSlot and rely on high ulimits

[allada]

ResumableFileSlot became to difficult to manage, instead of managing resources this way, we use much higher
DEFAULT_OPEN_FILE_PERMITS, set ulimit (when unix) and warn user if the limits are likely too low.

Breaking: Removed idle_file_descriptor_timeout_millis from config.

closes: #1288, #513, #1298, #527

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This change is 

[allada]

Reviewable status: 0 of 1 LGTMs obtained, and 0 of 21 files reviewed, and pending CI: Web Platform Deployment / ubuntu-24.04, pre-commit-checks, and 1 discussions need to be resolved (waiting on @aaronmondal)

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a discussion (no related file):
+@aaronmondal

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nativelink-worker/src/running_actions_manager.rs line 995 at r1 (raw file):

                            "Could not kill process",
                        );
                    } else {

fyi: This branch is the success case and the error was wrong, and it shouldn't be an ERROR.

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nativelink-store/tests/filesystem_store_test.rs line 1313 at r1 (raw file):

#[serial]
#[nativelink_test]
async fn update_with_whole_file_slow_path_when_low_file_descriptors() -> Result<(), Error> {

fyi: Removed this as it is an outlier and we mostly rely on ulimit now.

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nativelink-worker/tests/running_actions_manager_test.rs line 458 at r1 (raw file):

            arguments: vec!["touch".to_string(), "./some/path/test.txt".to_string()],
            output_files: vec!["some/path/test.txt".to_string()],
            environment_variables: vec![EnvironmentVariable {

fyi: sneaking these in on this PR.

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nativelink-worker/tests/running_actions_manager_test.rs line 1478 at r1 (raw file):

        assert_eq!(poll!(&mut run_action_fut), Poll::Pending);
        tokio::task::yield_now().await;
        match fs::metadata(&process_started_file).await {

fyi: This should fix this flaky test by waiting for the process to start. The test was fine before, but gave exit code 127 or 9 depending on the state of the process during the kill event.

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nativelink-util/src/buf_channel.rs line 375 at r1 (raw file):

                .recv()
                .await
                .err_tip(|| "During next read of buf_channel::take()")?;

fyi: Fixed typo.