Replace build.py with the xtask pattern

This is a rewrite of the Python build.py code in Rust. See
https://github.com/matklad/cargo-xtask for details of the xtask
pattern. Essentially it's a pattern for extending cargo with
project-specific commands. Using Rust gives all the usual benefits of
checking stuff at compile time, thorough error handling, ease of
testing, etc. It is more verbose though, so the LOC goes up a bit.

* Removed `build-std` settings from `.cargo/config` because we want to
  run `xtask` with the default compiler config. The various `cargo
  xtask` commands handle adding the build-std args where needed. This
  has the side effect of obsoleting the
  `uefi-macros/tests/cargo_wrapper` hack.

* The build subcommand now builds the whole workspace (except for xtask,
  since that implicitly has already been built). So no separate CI step
  to test that the `tmplate` package builds is needed.

* Dropped the `--verbose` option, just always print the commands being
  run since it's helpful info.

* Looked like there was some vestigial timeout code for the VM test but
  no timeout was set that I could see; added a timeout to the github
  workflow yaml instead.

Cargo.toml

@@ -10,6 +10,7 @@ exclude = [
     "uefi-macros/**",
     "uefi-services/**",
     "uefi-test-runner/**",
+    "xtask/**",
 ]
 description = "Safe and easy-to-use wrapper for building UEFI apps"
 repository = "https://github.com/rust-osdev/uefi-rs"
@@ -43,6 +44,7 @@ members = [
     "uefi-macros",
     "uefi-services",
     "uefi-test-runner",
+    "xtask",
 ]
 
 [patch.crates-io]