Fix #stats to prevent double formatting and use proper percent literal

[rmm5t]

What does it do?

• Fix #stats to prevent double formatting and use proper percent literal

What else do you need to know?

Note

1. Ruby 4 is not as forgiving as Ruby 3 when trying to print a percent literal.
2. The printf combined with the % operator was double formatting the string.

---

On Ruby 4.0, the spec suite failed with:

Failures:

  1) BloomFilter::CountingRedis a default CountingRedis instance should output current stats
     Failure/Error: expect { subject.stats }.not_to raise_error
     
       expected no Exception, got #<ArgumentError: malformed format string> with backtrace:
         # ./lib/bloomfilter/filter.rb:10:in 'String#%'
         # ./lib/bloomfilter/filter.rb:10:in 'BloomFilter::Filter#stats'
         # ./spec/counting_redis_spec.rb:44:in 'block (4 levels) in <top (required)>'
         # ./spec/counting_redis_spec.rb:44:in 'block (3 levels) in <top (required)>'
     # ./spec/counting_redis_spec.rb:44:in 'block (3 levels) in <top (required)>'

Issues

Fixes #53

Broken Screenshots