[Go] Unroll WriteUint64 and WriteInt64.
[Go] Unroll WriteUint64 and WriteInt64.

This enables both WriteUint64 and WriteInt64 to both be inlined as
well as implemented with a single assembly instruction. The current Go
compiler refuses to inline functions with for loops. The compiler is
also not smart enough to produce a single assembly instruction for the
for-loop.

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