Introspection is all you need

[louisinger]

This PR introduces Arkade Script, a way to run custom Bitcoin opcodes within VTXOs.

A VTXO's tapscript still require all existing rules, namely that tapscripts fall under the cooperative/unilateral script closures.

However, when submitting an Ark transaction, you may provide an additional Arkade script , along with its own witness, that will be evaluated in parallel. The VTXO tapscript that is executing this commits to it by tweaking the mandatory server key by a hash of this Arkade script.

<TWEAK(server,Hash(<arkade_script>))>
OP_CHECKSIGVERIFY

If evaluated successfully, Arkade signs the ark transaction with the tweaked key. Additionally, it provides an execution proof, which consists of the Arkade script, the Arkade witness, the tx, and a signature from the server on all prior items.

The custom opcodes (and the associated engine) are declared in a new package common/arkscript. This PR implements the following extra opcodes:

• OP_INSPECTINPUTOUTPOINT
• OP_INSPECTINPUTVALUE
• OP_INSPECTINPUTSCRIPTPUBKEY
• OP_INSPECTINPUTSEQUENCE
• OP_PUSHCURRENTINPUTINDEX
• OP_INSPECTOUTPUTVALUE
• OP_INSPECTOUTPUTSCRIPTPUBKEY
• OP_INSPECTVERSION
• OP_INSPECTLOCKTIME
• OP_INSPECTNUMINPUTS
• OP_INSPECTNUMOUTPUTS
• OP_TXWEIGHT
• OP_CAT
• OP_SUBSTR
• OP_LEFT
• OP_RIGHT
• OP_INVERT
• OP_AND
• OP_OR
• OP_XOR
• OP_2MUL
• OP_2DIV
• OP_MUL
• OP_DIV
• OP_MOD
• OP_LSHIFT
• OP_RSHIFT
• OP_CHECKSIGFROMSTACK
• OP_ADD64
• OP_SUB64
• OP_MUL64
• OP_DIV64
• OP_NEG64
• OP_LESSTHAN64
• OP_LESSTHANOREQUAL64
• OP_GREATERTHAN64
• OP_GREATERTHANOREQUAL64
• OP_SCIPTNUMTOLE64
• OP_LE64TOSCIPTNUM
• OP_LE32TOLE64
• OP_SHA256INITIALIZE
• OP_SHA256UPDATE
• OP_SHA256FINALIZE
• OP_ECMULSCALARVERIFY
• OP_TWEAKVERIFY

An example of a VtxoScript using introspection can be found in the TestSendToArkScriptClosure e2e test.

@Kukks @tiero @altafan please review

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[Kukks]

Let's add

• OP_TXID - pushes this tx's hash to the stack
• OP_DETERMINISTICRANDOM- https://github.com/uncomputable/bitcoin-notes/blob/master/op_deterministicrandom.md