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/Cargo.lock

@@ -1881,6 +1881,7 @@ name = "codex-utils-cargo-bin"
 version = "0.0.0"
 dependencies = [
  "assert_cmd",
+ "path-absolutize",
  "thiserror 2.0.17",
 ]
 
@@ -2845,7 +2846,6 @@ dependencies = [
  "anyhow",
  "codex-core",
  "codex-utils-cargo-bin",
- "path-absolutize",
  "rmcp",
  "serde_json",
  "tokio",