Allow Redis Connection to be Injected

[allcentury]

See issue #188 for details.

Prior to this change, pooled redis connections were hard to share across jobs.

Now you can inject your own redis connection into the intiailizer via
the redis_conn parameter.

[allcentury]

@ashmaroli friendly ping - does all look ok here?

[ashmaroli]

Sorry. This had slipped out of my radar..
However, I'll leave the merging to other maintainers here.

[lewispb]

+1 for this

[lewispb]

Minor point but my preference for the argument name would just be redis.

Suggested change

	@redis = options.fetch(:redis_conn, Redis.new(options))
	@redis = options.fetch(:redis, Redis.new(options))

[cardmagic]

FYI, the original classifier gem now has a pluggable storage system that makes Redis integration straightforward.

Instead of baking Redis directly into the gem, it provides a Classifier::Storage::Base protocol that you can implement for any backend. Here's the Redis example from the documentation:

class RedisStorage < Classifier::Storage::Base
  def initialize(redis:, key:)
    @redis, @key = redis, key
  end

  def write(data) = @redis.set(@key, data)
  def read = @redis.get(@key)
  def delete = @redis.del(@key)
  def exists? = @redis.exists?(@key)
end

Usage:

# Inject your own Redis connection (pooled or otherwise)
redis_storage = RedisStorage.new(redis: my_redis_pool.checkout, key: 'classifier:spam')

# Create classifier with storage
classifier = Classifier::Bayes.new('Spam', 'Ham')
classifier.storage = redis_storage

# Train and save
classifier.train(:spam, 'Buy now!')
classifier.save

# Or load existing classifier from storage
classifier = Classifier::Bayes.load(storage: redis_storage)

This approach lets you use connection pools, configure timeouts, or use any Redis client library you prefer - the gem doesn't dictate the connection management strategy.

See: https://github.com/cardmagic/classifier/blob/master/lib/classifier/storage/base.rb