Gemfile:
The pry gem is installed but does not seem to be used for anything.
Tests pass without it just fine.

Fixes #607

Remove pry from Gemfile as it is not used

```
/home/runner/work/i18n/i18n/test/backend/cache_test.rb:65: warning: assigned but unused variable - cache_key
```

Remove warning: assigned but unused variable

This makes introspecting the translations loaded by a file easier. Maintains backwards compatability as the block is optional.

This results in a performance increase, and reduced object allocation, when normalizing keys -

```ruby
report = Benchmark.ips do |x|
  x.report("concat") do
    ex = []
    ex.concat ['foo']
    ex.concat ['bar', 'baz']
    ex.concat ['quix']
    ex
  end
  x.report("splat") do
    [
      *['foo'],
      *['bar', 'baz'],
      *['quix']
    ]
  end
  x.compare!
Warming up --------------------------------------
              concat   129.103k i/100ms
               splat   243.963k i/100ms
Calculating -------------------------------------
              concat      1.176M (± 9.7%) i/s -      5.810M in   5.009251s
               splat      2.435M (±11.8%) i/s -     11.954M in   5.019257s

Comparison:
               splat:  2434746.6 i/s
              concat:  1176432.3 i/s - 2.07x  (± 0.00) slower
```

Minor `I18n.normalize_keys` improvement

LazyLoadable Backend

Add a version badge to README

…aults

…ith_current_locale

Allow overriding of entry resolving entry resolving separate from defaults