Migrate from ethers-v5 to viem

[piotr-roslaniec]

Type of PR:

• Refactor

Required reviews:

• 3

What this does:

• Replaces dependency on ethers-v5 with viem
• Introduces signer-provider separation with WalletClient and PublicClient

Why it's needed:

Explain how this PR fits in the greater context of the NuCypher Network.
E.g., if this PR address a nucypher/productdev issue, let reviewers know!

Notes for reviewers:

• This is just an initial draft
• Rebased over Add a tapir CI job #445 to keep this PR tested (can drop these commits if needed)
• Remove remainder of ethers usage
• Remove typechain usage (based on ethers)
• Use abitype/zod to validate functionAbi instead of relying on ethers
• Originally drafted in Migrate from ethers-v5 to viem #271

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[codecov-commenter]

Codecov Report

Attention: 36 lines in your changes are missing coverage. Please review.

Comparison is base (1a8c590) 88.00% compared to head (1fb32bd) 87.89%.

Files	Patch %	Lines
packages/taco/src/dkg.ts	33.33%	12 Missing ⚠️
packages/pre/src/policy.ts	42.85%	8 Missing ⚠️
packages/taco/src/taco.ts	82.05%	6 Missing and 1 partial ⚠️
packages/taco/src/conditions/context/providers.ts	92.20%	4 Missing and 2 partials ⚠️
packages/taco/src/tdec.ts	86.36%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #421      +/-   ##
==========================================
- Coverage   88.00%   87.89%   -0.12%     
==========================================
  Files          33       33              
  Lines        2702     2767      +65     
  Branches      233      239       +6     
==========================================
+ Hits         2378     2432      +54     
- Misses        293      300       +7     
- Partials       31       35       +4     

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[piotr-roslaniec]

Currently fails due to some incompatibility between viem EIP712 signer and verifier on Ursula's side

Error: Threshold of responses not met; TACo decryption failed with errors: {"0x210eeAC07542F815ebB6FD6689637D8cA2689392":"(<class 'nucypher.network.middleware.RestMiddleware.BadRequest'>, BadRequest('Invalid data provided for context variable: Invalid data provided for \":userAddress\"; KeyError - \\'name\\''), 
// abbreviated