Use `jobslot` instead of dep `jobserver`

[NobodyXu]

Signed-off-by: Jiahao XU [email protected]

This PR replaces dep jobserver with a fork jobslot.

Advantages over jobserver?

• jobslot contains bug fix for Client::configure is unsafe
• jobslot removed use of signal handling in the helper thread on unix
• jobslot uses winapi on windows instead of manually declaring bindings (some of the bindings seem to be wrong)
• jobslot uses getrandom on windows instead of making homebrew one using raw windows api