feature: Improve timestamp serialization, add device_data to MinerData, and use enums for device information

[UpstreamData]

• Add field device_info to MinerData, containing make, model, and firmware
• Make make, model, and firmware enum variants.
• Remove MinerData.model and MinerData.make field
• Improve timestamp serialization by moving datetime.datetime instance to MinerData._datetime, and exposing 2 new datetime formats, iso format for MinerData.datetime, and a unix timestamp in MinerData.timestamp.
• Add expected_fans to miner data.

[UpstreamData]

Fixes #133 Fixes #136

[vijendtra]

@UpstreamData when you plan to release these changes ?

[UpstreamData]

Just waiting on one of the other contributors to review as a sanity check, this is a fairly large change so just want to make sure it's all correct.