make OP_RETURN data format safe and efficient

[Alrighttt]

['faucet.drip', ([1], [1, 1]), {}, '03a8339e98111ee9dc74a956164e6507a67005f4a2c45c0481f1b9d7c3c7d5fd9a', '03a8339e98111ee9dc74a956164e6507a67005f4a2c45c0481f1b9d7c3c7d5fd9a']"

If a pubkey is stored like this in OP_RETURN by pycctx, it it first being converted to ascii prior to being added to the OP_RETURN. This results in the data taking twice as much space.

[ssadler]

Currently, OP_RETURN contains and ascii blob which is just the result of repr called on the params, and it is "parsed" with eval, which is highly unsafe.

This should be replaced with a binary format with automatic deduplication and safe parsing.