Lazy-load digest dependency

[theodorton]

I've experienced some pain in running spring and bootsnap together. Symptom is a Gem::LoadError thrown when there are conflicting versions of digest installed:

You have already activated digest 3.0.0, but your Gemfile requires digest 3.1.0. Since digest is a default gem, you can either remove your dependency on it or try updating to a newer version of bundler that supports digest as a default gem. (Gem::LoadError)

Since digest is now being included as a default gem in Ruby, it's hard to circumvent the issue without locking digest to an older version.

The problem seems to disappear when deferring the require call.

Relevant issues to similar problems:
#603
#616

[Tonkpils]

@rafaelfranca any chance we can backport this to the Spring 3 release? Upgrading to Rails 7 seems to trigger this failure and a few gems like spring-watcher-listen have a restriction on spring of < 4.0.

[yjukaku]

It would be helpful as well for us to have this backported to Spring 3.