tbc: cache raw block bytes instead of decoding and re-encoding

[joshuasing]

Confirmation

• I have checked for similar issues.

Problem

TBC currently uses btcd's wire package to decode and encode blocks.
This can result in data loss if the wire package does not decode certain data, as it will not retain data it doesn't know to retain.

Suggested solution

Instead of decoding and re-encoding blocks in TBC, we should cache the raw block bytes and decode it once, then store the raw bytes for later use.

Additional Information

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