Replace build-dir.py with zcurses build-dir

Update the build-dir shell function to usage zcurses instead of the
Python pick package to interactively select build directories, this
results in a more responsive user experience. Add argument parsing to
handle various use cases. Add prompt when the build command for the
selected build directory could not be detected, allowing the user to
specify the desired build command.

```
usage: build-dir [-h] [--build] [<directory>]

Find and select the current build directory interactively.

positional arguments:
  <directory> the build directory to select

optional arguments:
  -h, --help  show this help message and exit
  --build     invoke a build after selection
```

build/build.plugin.zsh

@@ -35,9 +35,9 @@ optional arguments:
   -h, --help  show this help message and exit
   --build     invoke a build after selection
 EOF
-    exit
+    return
   fi
-  error() { echo "\e[31merror:\e[0m $1"; exit 1 }
+  error() { echo "\e[31merror:\e[0m $1"; return 1 }
   local build_dir
   if [[ ${#*} -gt 1 ]]; then
     echo $usage