## 🔄 Changes Summary

This PR completely removes the logic around setting `Metadata` field on
certificates since it will no longer be used to determin block ranges on
`aggsender`.

`Metadata` field will still exist on certificates, but it will no longer
be used, and a `ZeroHash` will be enforced instead.

## ⚠️ Breaking Changes
NA

## 📋 Config Updates
NA

## ✅ Testing
- 🤖 **Automatic**: `aggkit` CI

## 🐞 Issues
#799

## 🔗 Related PRs
#838
#839
#846

## 🔄 Changes Summary

Enable the AggSender to work with multiple validator nodes in a
committee-based validation system. The implementation includes validator
services, multisig committee management, certificate validation
improvements, and enhanced gRPC communication protocols.

**Multisig Committee Support:** 
- Added `MultisigCommittee` type to manage signer sets and enforce
signature thresholds.
- Signers are represented as `SignerInfo` structs with both address and
URL for improved context and error reporting.
- Committee construction validates non-empty membership and non-zero
threshold, preventing misconfiguration.
- Dynamic signer management: methods for adding signers, duplicate
checks by address and URL.

**Aggsender Validator Refactor:**
- The Aggsender certificate validation flow was refactored to integrate
multisig logic.
- The multisig validation logic is applicable to both `PP` and `FEP`
certificates.
- Certificate validation now checks for contiguous certificates, last L2
block, and settlement status using new queries.
- Import bridge exit proof verification is handled via new logic using
`verifyClaimProofs`, ensuring only valid proofs pass.

**Certificate Metadata removal:**
- It is gone from the agglayer and therefore it is not sent anymore from
the aggsender either.
- Only thing worth noting is that, when calculating `CertificateID`,
instead of metadata field, which was used previously, we now use
`ZeroHash`.

**Smart contracts integration:**
- **AggchainFEP contract:** Removed querying of `TrustedSequencer`
address and rely on the signers committee instead
- **AggchainBase contract:** Retrieve the multisig committee from the
`AggchainBase` contract

**Agglayer integration:**
- Invoke the `GetNetworkState` API from agglayer to get the latest
settled imported bridge exit info.
- Multisig is populated into the certificate and sent to the Agglayer's
`SendCertificate` gRPC endpoint

## ⚠️ Breaking Changes
- 🛠️ **Config**: Make sure that `Mode` on the `Validator` and
`AggSender` are the same.
- 🔌 **API/CLI**: `aggkit` version (`v0.7.0`) that supports `multisig`
will now require updated contracts to run. At least version
`v12.1.0-rc.3` of `agglayer-contracts`, and a new version of `agglayer`
which supports `multisig`, which is the `v0.4.0` of `agglayer`.
- 🗑️ **Deprecated Features**: Aggsender Phase II validator signing logic

## 📋 Config Updates
- Added `AggSender.RequireCommitteeMembershipCheck = false` parameter,
which defines if a check on `aggsender proposer` startup will be
performed to see if the proposer is in the `multisig` committee.
- Added `Validator.RequireCommitteeMembershipCheck =
{{AggSender.RequireCommitteeMembershipCheck}}` parameter, which defines
if a check on `aggsender validator` startup will be performed to see if
the validator is in the `multisig` committee.
- Added `Validator.Mode = "PessimisticProof"` parameter, which acts the
same as the `AggSender.Mode`. It tells the validator that the network is
a `PP` network or an `FEP` network. It has to be the same as on
`aggsender proposer`.
- Added `Validator.FEPConfig.SovereignRollupAddr =
"{{AggSender.SovereignRollupAddr}}" parameter which is the address of
the `AggchainFEP` rollup on L1 for given network for which validator is
running.
- Added `Validator.FEPConfig.RequireNoBlockGap =
{{AggSender.RequireNoFEPBlockGap}}, which acts the same as the given
paremeter on `AggSender` (proposer) config, and tells the validator if
gaps in blocks in certificates are allowed in `FEP` network.

```toml
[AggSender]
RequireCommitteeMembershipCheck = false

[Validator]
# PessimisticProof or AggchainProof
Mode = "PessimisticProof"
RequireCommitteeMembershipCheck = {{AggSender.RequireCommitteeMembershipCheck}}
[Validator.FEPConfig]
	SovereignRollupAddr = "{{AggSender.SovereignRollupAddr}}"
	RequireNoBlockGap = "{{AggSender.RequireNoFEPBlockGap}}"
```

## ✅ Testing
- 🤖 **Automatic**: `aggkit` CI
- 🖱️ **Manual**: [Optional: Steps to verify]

## 🐞 Issues
- Closes #792 
## 🔗 Related PRs
- #814
- #832
- #838
- #839
- #843
- #842
- #846
- #858
- #847
- #865
- #861
- #863
- #875
- #876
- #881
- #877
- #898
- #920
- #913
- #926
- #945
- #951
- #954
- #957
- #955
- #974
- #978
- #985
- #989
- #984
- #998
- #1017
- #1028
- #1034
- #1024
- #1052
- #1067
- #1068
- #1050
- #1071
- #1072
- #1060
- #1087
- #1077
- #1073

---------

Co-authored-by: Goran Rojovic <[email protected]>
Co-authored-by: Goran Rojovic <[email protected]>
Co-authored-by: Joan Esteban <[email protected]>
Co-authored-by: Rachit Sonthalia <[email protected]>
Co-authored-by: Arpit Temani <[email protected]>
Co-authored-by: Copilot <[email protected]>