Memoize Bundler::LazySpecification#hash to improve performance

[technicalpickles]

What was the end-user or developer problem that led to this PR?

In local testing, we found require 'bundler/setup' took 1.8 seconds to load.
I started profiling and looking at flamegraphs for this code, and found
a surprising amount of time in this method.

What is your fix for the problem, implemented in this PR?

Memoizing this specific method reduced time by 0.7 to 1.1 seconds, a 38%
improvement.

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags

cc @ngan who I paired with on this

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[technicalpickles]

I'm attaching the stackprof data as JSON, which can be viewed with speedscope

bundler-test.txt
(is JSON despite name)

And here's the scaffold I used to run it:

require 'benchmark'
require 'stackprof'

result = Benchmark.measure  do
  StackProf.run(mode: :wall, raw: true, out: 'bundler-test.dump', ignore_gc: true) do
    require 'bundler/setup'
  end
end

puts result

[technicalpickles]

Looks like @ngan beat me too it 😅 This is a subset of #5534

[deivid-rodriguez]

Yes! And also I think #5533 should make this unnecessary, can you verify?

[technicalpickles]

Confirmed that #5533 would address this case 🚀