enable "thin LTO" in release profile

docs/notes/2.32.x.md

@@ -20,6 +20,8 @@ The plugin API's `Get()` and `MultiGet()` constructs, deprecated in 2.30, are no
 
 ### General
 
+The rust engine of Pants is now compiled with ["thin" Link Time Optimization](https://nnethercote.github.io/perf-book/build-configuration.html#link-time-optimization).  This results in a slightly smaller binary and a few percentage points of improved performance on certain workloads.
+
 #### Internal Python Upgrade
 
 The version of Python used by Pants itself has been updated to [3.14](https://docs.python.org/3/whatsnew/3.14.html). To support this, the [Pants Launcher Binary](https://www.pantsbuild.org/blog/2023/02/23/the-pants-launcher-binary-a-much-simpler-way-to-install-and-run-pants) (also known as [`scie-pants`](https://github.com/pantsbuild/scie-pants/)) now has a minimum version of `0.13.0`. To update to the latest launcher binary, either:

src/rust/Cargo.toml

@@ -4,6 +4,7 @@
 debug = 1
 # Optimise for the speed of our binary, rather than the speed of compilation.
 codegen-units = 1
+lto = "thin"
 
 [workspace]
 resolver = "2"