Add frozen_string_literal: true comment to all files

[bentranter]

Attempts to address #289

While I thought the plan for Ruby 3 was to make frozen_string_literal: true the default, I guess that wasn't the case (see Matz's comment about it). This change adds all of the magic frozen_string_literal: true comments to the top of the file.

When run in IRB on main, this is what I see when trying to use a Ractor to print DropletKit's version:

 $ irb -I lib -r droplet_kit
irb(main):001:0> r = Ractor.new { puts DropletKit::VERSION }
<internal:ractor>:267: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
#<Thread:0x00007fa85987e160 run> terminated with exception (report_on_exception is true):
(irb):1:in `block in <main>': can not access non-shareable objects in constant DropletKit::VERSION by non-main Ractor. (Ractor::IsolationError)
=> #<Ractor:#2 (irb):1 terminated>

which seems to be the error in the linked issue.

This is what I see on this branch:

$ irb -I lib -r droplet_kit
irb(main):001:0> r = Ractor.new { puts DropletKit::VERSION }
<internal:ractor>:267: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
3.16.0
=> #<Ractor:#2 (irb):1 terminated>

Suggesting that it resolves the issue.

I also fixed the whitespace + formatting of a few files. It probably wasn't necessary to add the comment to all of the tests, but I did this with the magic_frozen_string_literal gem which did that by default, so I figured I'd leave it.

[andrewsomething]

I thought the plan for Ruby 3 was to make frozen_string_literal: true the default

This comment it's self is three years old now, so not sure of the current state of affairs, but looks like matz decided not to do this.

So I officially abandon making frozen-string-literals default (for Ruby3).

https://bugs.ruby-lang.org/issues/11473#note-53

[andrewsomething]

👍 Makes sense