chore: replace regex with regex-lite, where appropriate (#1200)

As explained on https://crates.io/crates/regex-lite, `regex-lite` is a
lighter alternative to `regex` and seems to be sufficient for our
purposes.

codex-rs/Cargo.lock

@@ -567,7 +567,6 @@ version = "0.0.0"
 dependencies = [
  "anyhow",
  "pretty_assertions",
- "regex",
  "serde_json",
  "similar",
  "tempfile",
@@ -682,7 +681,7 @@ dependencies = [
  "log",
  "multimap",
  "path-absolutize",
- "regex",
+ "regex-lite",
  "serde",
  "serde_json",
  "serde_with",
@@ -757,7 +756,7 @@ dependencies = [
  "pretty_assertions",
  "ratatui",
  "ratatui-image",
- "regex",
+ "regex-lite",
  "serde_json",
  "shlex",
  "strum 0.27.1",
@@ -3323,6 +3322,12 @@ dependencies = [
  "regex-syntax 0.8.5",
 ]
 
+[[package]]
+name = "regex-lite"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "53a49587ad06b26609c52e423de037e7f57f20d53535d66e08c695f347df952a"
+
 [[package]]
 name = "regex-syntax"
 version = "0.6.29"