fix(transparent): check coinbase data is at least 2 bytes long

[teor2345]

Motivation

zcashd requires coinbase data that's 2-100 bytes long:
https://github.com/zcash/zcash/blob/d8c818bfa507adb845e527f5beb38345c490b330/src/main.cpp#L1697-L1698

But Zebra accepts coinbase data that's 1-100 bytes long:

zebra/zebra-chain/src/transparent/serialize.rs

Line 250 in fa07156

if data.len() > MAX_COINBASE_DATA_LEN {

zebra/zebra-chain/src/transparent/serialize.rs

Line 74 in fa07156

(Some(op_n @ 0x51..=0x60), len) if len >= 1 => Ok((

Specifications

There is an upcoming change to the Zcash specifications:
zcash/zips#589

Related Work

We might want to merge these height changes first, they could cause a merge conflict:

• Support large block heights #3401

[ftm1000]

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