fix: make the find_resource! macro responsible for the absolutize() call (#8884)

https://github.com/openai/codex/pull/8879 introduced the
`find_resource!` macro, but now that I am about to use it in more
places, I realize that it should take care of this normalization case
for callers.

Note the `use $crate::path_absolutize::Absolutize;` line is there so
that users of `find_resource!` do not have to explicitly include
`path-absolutize` to their own `Cargo.toml`.

codex-rs/exec-server/tests/common/Cargo.toml

@@ -11,7 +11,6 @@ path = "lib.rs"
 anyhow = { workspace = true }
 codex-core = { workspace = true }
 codex-utils-cargo-bin = { workspace = true }
-path-absolutize = { workspace = true }
 rmcp = { workspace = true }
 serde_json = { workspace = true }
 tokio = { workspace = true }