feat: introduce --compute-indices flag to codex-file-search (#1419)

This is a small quality-of-life feature, the addition of
`--compute-indices` to the CLI, which, if enabled, will compute and set
the `indices` field for each `FileMatch` returned by `run()`. Note we
only bother to compute `indices` once we have the top N results because
there could be a lot of intermediate "top N" results during the search
that are ultimately discarded.

When set, the indices are included in the JSON output when `--json` is
specified and the matching indices are displayed in bold when `--json`
is not specified.

codex-rs/file-search/Cargo.toml

@@ -16,5 +16,6 @@ anyhow = "1"
 clap = { version = "4", features = ["derive"] }
 ignore = "0.4.23"
 nucleo-matcher = "0.3.1"
+serde = { version = "1", features = ["derive"] }
 serde_json = "1.0.110"
 tokio = { version = "1", features = ["full"] }