docs: Add build script to test templates (#6510)

## Description

Closes https://github.com/FuelLabs/sway/issues/3026

Adds a build script to the test templates that runs prior to the tests
when `cargo test` is run. This makes it so users who copy this template
don't have to run `forc build` prior to `cargo test`

## Checklist

- [ ] I have linked to any relevant issues.
- [ ] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [ ] If my change requires substantial documentation changes, I have
[requested support from the DevRel
team](https://github.com/FuelLabs/devrel-requests/issues/new/choose)
- [ ] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [ ] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [ ] I have requested a review from the relevant team or maintainers.

---------

Co-authored-by: K1-R1 <77465250+K1-R1@users.noreply.github.com>
Co-authored-by: Joshua Batty <joshpbatty@gmail.com>

docs/book/src/testing/testing-with-rust.md

@@ -74,18 +74,21 @@ Let's have a look at the result:
 $ tree .
 ├── Cargo.toml
 ├── Forc.toml
+├── build.rs
 ├── src
 │   └── main.sw
 └── tests
     └── harness.rs
 ```
 
-We have two new files!
+We have three new files!
 
 - The `Cargo.toml` is the manifest for our new test harness and specifies the
   required dependencies including `fuels` the Fuel Rust SDK.
 - The `tests/harness.rs` contains some boilerplate test code to get us started,
   though doesn't call any contract methods just yet.
+- The `build.rs` is a build script that compiles the Sway project with `forc build`
+  whenever `cargo test` is run.
 
 ### 4. Build the forc project
 
@@ -111,6 +114,7 @@ $ tree
 ├── Cargo.toml
 ├── Forc.lock
 ├── Forc.toml
+├── build.rs
 ├── out
 │   └── debug
 │       ├── my-fuel-project-abi.json

templates/sway-predicate-test-rs/template/build.rs

@@ -0,0 +1,7 @@
+//! This build script is used to compile the sway project using `forc` prior to running tests.
+
+use std::process::Command;
+
+fn main() {
+    Command::new("forc").args(&["build"]).status().unwrap();
+}

templates/sway-script-test-rs/template/build.rs

@@ -0,0 +1,7 @@
+//! This build script is used to compile the sway project using `forc` prior to running tests.
+
+use std::process::Command;
+
+fn main() {
+    Command::new("forc").args(&["build"]).status().unwrap();
+}

templates/sway-test-rs/template/build.rs

@@ -0,0 +1,7 @@
+//! This build script is used to compile the sway project using `forc` prior to running tests.
+
+use std::process::Command;
+
+fn main() {
+    Command::new("forc").args(&["build"]).status().unwrap();
+}