Add comprehensive JSDoc documentation to signing module functions

[theref]

Overview

The signing module has JSDoc for the main signUserOp function, but other important functions lack documentation. This makes it harder for developers to understand and use the module effectively.

Current State

• ✅ signUserOp has comprehensive JSDoc
• ❌ aggregateSignatures has no JSDoc
• ❌ setSigningCohortConditions has no JSDoc
• ❌ Type definitions lack documentation

Tasks

Add JSDoc comments to the following in packages/taco/src/sign.ts:

1. aggregateSignatures function (lines 38-54):

/**
 * Aggregates multiple signatures into a single concatenated signature.
 * @param signaturesByAddress - Map of addresses to TacoSignature objects
 * @param threshold - Number of signatures to include in aggregation
 * @returns Concatenated hex string of signatures
 */

2. setSigningCohortConditions function (lines 179-201):

/**
 * Sets the signing conditions for a cohort on the blockchain.
 * @param provider - JSON-RPC provider for blockchain interaction
 * @param domain - The TACo domain
 * @param conditions - The conditions to set for the cohort
 * @param cohortId - The ID of the signing cohort
 * @param chainId - The blockchain chain ID
 * @param signer - Ethereum signer to execute the transaction
 * @returns Promise resolving to the contract transaction
 */

3. SignResult type (lines 32-36):

/**
 * Result of a signing operation.
 * @property messageHash - The hash of the message that was signed
 * @property aggregatedSignature - The aggregated signature from threshold signers
 * @property signingResults - Individual signing results from each Ursula node
 */

Documentation Standards

• Follow the existing JSDoc style used in signUserOp
• Include all parameters with types and descriptions
• Document return values
• Add @throws annotations where applicable
• Include example usage if helpful

Definition of Done

• [ ] All public functions have JSDoc comments
• [ ] All exported types have JSDoc comments
• [ ] Documentation follows consistent style
• [ ] Documentation is accurate and helpful
• [ ] No linting errors related to documentation