new binary handling

[ChristopherBiscardi]

• simplify binary handling
• split out functions for easier testability and dev/prod behavior
• add version to binary dir path

enables disallowing the installation of the toast binary from a url with TOAST_PREVENT_INSTALL and specifying the binary location with TOAST_BINARY

TOAST_PREVENT_INSTALL=true TOAST_BINARY=/Users/chris/github/toastdotdev/toast/target/debug/toast toast incremental .