feat: add ability to spawn child process with pty (#7077)

### Description

This PR adds, but doesn't hook up, the ability to spawn a child process
hooked up to a pseudo terminal.

I *highly* suggest reviewing each commit on its own. I tried my best to
split out prefactoring work from any feature work.

### Testing Instructions

Adapt unit tests to cover all of them. It will be noted that switching
to use a PTY does affect what programs output and so the tests were made
to not check for identical output, but just that we got the expected
output.
Closes TURBO-2128

crates/turborepo-lib/Cargo.toml

@@ -64,6 +64,7 @@ notify = "5.1"
 path-clean = "1.0.1"
 petgraph = { workspace = true }
 pidlock = { path = "../turborepo-pidlock" }
+portable-pty = "0.8.1"
 prost = "0.11.6"
 rand = { workspace = true }
 reqwest = { workspace = true, default-features = false, features = ["json"] }