feat(protocol): add special logics for alpha-2 testnet

[dantaik]

For alpha-2 testnet, the network only allows an special address to propose but anyone to prove. This is the first step of testing the tokenomics. In this PR, a special prover can skip ZKP verification if the ZKP is empty which is to handle unexpected ZKP circuit bugs.

I also rebranded TkoToken as a Taiko USD stablecoin token, so we don't have to create a marketplace for it and can incentivize people with 1tkUSD == 1 USDT/USDC.

This PR shall be reverted once alpha-2 is shutdown.

[codecov]

Codecov Report

Merging #12987 (f643d2d) into main (dd389be) will decrease coverage by 0.18%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main   #12987      +/-   ##
==========================================
- Coverage   66.32%   66.15%   -0.18%     
==========================================
  Files         113      112       -1     
  Lines        3050     3052       +2     
  Branches      357      363       +6     
==========================================
- Hits         2023     2019       -4     
- Misses        951      957       +6     
  Partials       76       76              

Flag	Coverage Δ		*Carryforward flag
bridge-ui	92.61% <ø> (ø)		Carriedforward from 6c7beac
protocol	58.90% <50.00%> (-0.33%)	⬇️
relayer	68.92% <ø> (ø)		Carriedforward from 6c7beac
ui	100.00% <ø> (ø)		Carriedforward from 6c7beac

*This pull request uses carry forward flags. Click here to find out more.

Impacted Files	Coverage Δ
packages/protocol/contracts/L1/TkoToken.sol	84.21% <ø> (ø)
packages/protocol/contracts/L1/libs/LibProving.sol	0.00% <0.00%> (ø)
...ckages/protocol/contracts/L1/libs/LibProposing.sol	9.23% <100.00%> (+4.39%)	⬆️
...s/protocol/contracts/bridge/libs/LibBridgeSend.sol	76.19% <0.00%> (-23.81%)	⬇️
packages/protocol/contracts/bridge/Bridge.sol	56.00% <0.00%> (-3.38%)	⬇️
packages/protocol/contracts/bridge/EtherVault.sol	100.00% <0.00%> (ø)
packages/protocol/contracts/bridge/TokenVault.sol	60.86% <0.00%> (ø)
packages/protocol/contracts/libs/LibTrieProof.sol	0.00% <0.00%> (ø)
...ckages/protocol/contracts/L1/libs/LibVerifying.sol	13.33% <0.00%> (ø)
... and 13 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more