CHIA-255: implement CHIP-34

[arvidn]

this PR is best reviewed one commit at a time.

It implements CHIP-34.

new operators

There are 3 new operators enabled under softfork 1:

operator	opcode
base64url_encode	62
base64url_decode	63
keccak256	64

cost

operator	base cost	per argument	per byte
base64url_encode	40	130	2
base64url_decode	400	-	2
keccak256	50	160	2

As always, there's also a cost of 10 per byte that's allocated for the return value.

activation

Since this is a softfork, the extension will only be available when the ENABLE_BASE64 flag is set, which it will be after the softfork activates.

The operators will only be available for programs (<prg>) executing under (softfork <cost> 1 <prg> <arg>)

hard fork

There's an option to hard-fork these operators out of the softfork-guard by specifying ENABLE_BASE64_OPS_OUTSIDE_GUARD.

keccak-256

The test vectors are generated using the python wheel from eth_hash.auto import keccak.

[coveralls-official]

Pull Request Test Coverage Report for Build 9096480917

Details

• 90 of 92 (97.83%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.05%) to 94.214%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/base64_ops.rs	61	62	98.39%
src/chia_dialect.rs	7	8	87.5%

Totals
Change from base Build 9096453504:	0.05%
Covered Lines:	5895
Relevant Lines:	6257

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💛 - Coveralls

[Rigidity]

Looks good to me (feel free to resolve these minor comments)