Use precomputed tables

[SethDusek]

Use pre-computed multiplication tables for generator where possible (secret key -> pk, generating public image of nonce in signing/verification, etc). Also pre-compute DlogProverInput.public_image() to avoid repeated EC operations in signing (helps performance when there are many secrets in Wallet).

Some benchmarks (Wallet with 1000 secrets, signing N inputs):

• cachedpk is with only eagerly-evaluated public image (a410eaf)
• precomputed+cachedpk uses generator table optimization + cachedpk
• Final is the result of all optimizations, along with some other smaller optimizations
  

Some small improvements to verification as well, tested on dbd86fdce57f3a5124e88ec1ee4b7289e450e059e21a74c303bf13bf0b924945, time to verify is down from 0.2s to 0.17s

[coveralls]

Pull Request Test Coverage Report for Build 12594306876

Details

• 62 of 69 (89.86%) changed or added relevant lines in 16 files are covered.
• 11 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.002%) to 78.463%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ergo-lib/src/chain/transaction/unsigned.rs	0	1	0.0%
ergotree-interpreter/src/eval/create_provedlog.rs	0	1	0.0%
ergotree-interpreter/src/sigma_protocol/private_input.rs	14	15	93.33%
ergo-lib/src/wallet/ext_secret_key.rs	9	13	69.23%

Files with Coverage Reduction	New Missed Lines	%
ergotree-interpreter/src/sigma_protocol/private_input.rs	1	90.32%
ergotree-ir/src/serialization/types.rs	10	82.52%

Totals
Change from base Build 12589822362:	0.002%
Covered Lines:	11079
Relevant Lines:	14120

---

💛 - Coveralls