test: organize integration tests into single crate

Put all integration tests in a single crate, and organized in modules.

This is similar to what was done in `cargo` repository:
https://github.com/rust-lang/cargo/pull/5022#issuecomment-364691154

```
$ rustup show
stable-x86_64-unknown-linux-gnu (default)
rustc 1.69.0 (84c898d65 2023-04-16)
```

Run on a recent high-end laptop:
12th Gen Intel(R) Core(TM) i9-12900HK

Original (multiple integration binaries):

- `cargo clean && cargo test --no-run`: 62.893s
- `cargo clean && cargo build --lib`: 54.959s
- `cargo clean && cargo build --bins`: 55.933s
- `cargo test --no-run` (after `cargo build`): 14.472s
- `cargo test` (after `cargo test --no-run`): 1.786s
- `du -hs target/`: 4.2G

After (ironrdp-testsuite):

- `cargo clean && cargo test --no-run`: 41.157s (crates with no tests are ignored)
- `cargo clean && cargo build --lib`: 53.983s
- `cargo clean && cargo build --bins`: 54.482s
- `cargo test --no-run` (after `cargo build`): 12.915s
- `cargo test` (after `cargo test --no-run`): 0.240s
- `du -hs target/`: 3.4G

Absolute diff:
- `cargo clean && cargo test --no-run`: -21.736s
- `cargo clean && cargo build --lib`: -0.976s
- `cargo clean && cargo build --bins`: -1.451s
- `cargo test --no-run` (after `cargo build`): -1.557s
- `cargo test` (after `cargo test --no-run`): -1.546s
- `du -hs target/`: -0.8G

Relative diff (%):
- `cargo clean && cargo test --no-run`: -34.5%
- `cargo clean && cargo build --lib`: -1.77%
- `cargo clean && cargo build --bins`: -2.59%
- `cargo test --no-run` (after `cargo build`): -10.7%
- `cargo test` (after `cargo test --no-run`): -86.5%
- `du -hs target/`: -19.0%

crates/ironrdp-session-generators/Cargo.toml

@@ -5,6 +5,10 @@ edition = "2021"
 description = "`proptest` generators for `ironrdp-session` types"
 publish = false
 
+[lib]
+doctest = false
+test = false
+
 [dependencies]
 ironrdp-session.workspace = true
 ironrdp-pdu-generators.workspace = true

crates/ironrdp-session-generators/src/lib.rs

@@ -1,14 +1 @@
-pub fn add(left: usize, right: usize) -> usize {
-    left + right
-}
 
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
-    }
-}