feat(account): implement configureMultisig()

[Andreschuks101]

Summary

Resolves #57 - implements the configureMultisig() function that configures multi-signature security on a Stellar account using the Stellar SDK.

What was added

src/multisig/validation.ts

• Defines MultisigConfig, SignerConfig, and Thresholds interfaces
• Exports a custom ValidationError class (extends Error, restores prototype chain)
• validateMultisigConfig(config) runs three checks before any network call:
  1. masterKey is a valid Ed25519 public key (StrKey.isValidEd25519PublicKey)
  2. Every signer.publicKey is a valid Ed25519 public key
  3. Sum of all signer weights is strictly greater than thresholds.high

src/multisig/builder.ts

• configureMultisig(config, server, networkPassphrase):
  1. Runs validateMultisigConfig (throws before touching the network on bad input)
  2. Calls server.loadAccount(accountId) to get current sequence number
  3. Builds one TransactionBuilder with SetOptions operations for thresholds and signers
  4. Signs with Keypair.fromSecret(masterKey)
  5. Submits via server.submitTransaction(transaction)
  6. Returns { accountId, transactionHash }

src/multisig/index.ts

• Barrel re-export for clean imports

Test coverage (src/multisig/tests/configureMultisig.test.ts)

Scenario	What is asserted
Invalid signer publicKey	ValidationError thrown, message contains the bad key
Invalid masterKey	ValidationError thrown
Total weight <= high threshold	ValidationError thrown
Total weight > high threshold	No error
Happy path (mocked server)	Returns { accountId, transactionHash }
loadAccount called correctly	Mock assertion
submitTransaction called once	Mock assertion
loadAccount rejection propagates	Error re-thrown

All server calls are mocked with jest.fn() so tests run fully offline.

How to run tests

npm test

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[amina69]

@Andreschuks101 kindly make your pr to the develop branch, see the contributing.md for directions

[amina69]

@Andreschuks101 read the contributing.md, make your pr to develop branch

[amina69]

@Andreschuks101 kindly fix this audit error, pipeline not fully passing