### Purpose:
This is a prerequisite for #2288. The new grace period means that if we
didn't update the date from the cached responses, entitlements would
become stale and expired after 3 days.
### Changes:
- Added `HTTPResponseBody.copy(with newRequestDate:)` to be able to
modify responses from the header request date
- `CustomerInfo` implements this method to modify its request date
- Added `HTTPResponse.requestDate` to be able to keep track of the
request date from the server
- Added `VerificationResult.from(cache:response:)` to determine the most
restrictive verification result based on what's cached or checked from a
response
- Added `HTTPResponse.copy(with:)` to modify the verification result of
a response using the previous method
- `HTTPClient` now uses the most restrictive verification result
- `HTTPClient` updates request date from server responses or cached
responses (unless verification failed). This was the missing piece for
#2288.
### Tests:
- Verify that `ETagManager` does not use an ETag if verification was
previously not enabled
- Verify that `ETagManager` returns the request date from the server
when returning a cached response
- Verify that `HTTPClient` updates the request date from the server or
from a cached response
- Verify that `HTTPClient` does not update request date if verification
failed
- Tests for `HTTPResponse` request date parsing
- Test for `CustomerInfoResponseHandler` updating request date
- Tests for `CustomerInfo.copy(with newRequestDate:)`
### Other smaller changes:
- Moved `CustomerInfo.asData()` into `Encodable.asJSONEncodedData()`
- Renamed `requestTime` to `requestDate` everywhere for consistency
### Motivation:
Initially I wanted to make `SubscriberAttribute.asDictionary` work using `Codable`. However, this isn't the right refactor because we need the actual raw types to be encoded inside `UserDefaults`.
At least this refactor provides several improvements:
### Changes:
- `SubscriberAttribute` now has value semantics
- ⚠️ `SubscriberAttribute.isSynced` used to be mutable, with reference semantics, which was dangerous
- `SubscriberAttribute: Equatable` implementation is now automatic
- Cleaned up `SubscriberAttribute.asDictionary` implementation, extracting keys into an `enum`
- Moved `Dictionary` -> `SubscriberAttribute` creation to the type itself
- ⚠️ `SubscriberAttribute.init(dictionary:)` returns an `Optional` instead of using force-unwrap, avoiding potential crashes
- Added more serialization / deserialization tests
- Removed `SubscriberAttributesMarshaller` and moved method into `SubscriberAttribute` extension
- Moved `SubscriberAttributeDict` into `SubscriberAttribute.Dictionary`
NachoSoto