Fix caching streams and cache lifetimes.

[EAnushan]

I found some issues with the way caching is implemented at the moment.

1. Serializing the response stream causes the stream to seek to the end. You need to rewind the stream or the caller code will receive an empty body.
2. All entries are being cached forever. I forwarded a lifetime through Doctrine's Cache interface.

[EAnushan]

I think the tests may need to be updated.

[Kevinrob]

Thank for your contribution!
For the stream, it's alright!

But for the TTL, you miss something with 2 situations (the broken tests):

• Cache-Control: stale-if-error=XXX (Kevinrob\GuzzleCache\HeaderExpireTest::testStaleIfErrorHeader)
• HTTP re-validation

Can you please make a PR with only the stream issue for a rapid merging?
For the TTL, I suggest to add a method in CacheEntry like getTTL(). Like that, we can keep the logic of lifetime in it. (infinite TTL if some conditions (re-validation, etc.))

[Kevinrob]

Or if you are okay, I can do it myself after the merge. :)

[EAnushan]

I think I will leave this up to you as I haven't read the entire RFC yet for HTTP caching if that's okay with you?

[Kevinrob]

It's done!
Thank again for your help!

[EAnushan]

Thank you =)