fix(types): widen constructor to accept ISigner (parent's contract)

[AlonzoRicardo]

Summary

The abstract WalletManager (in @tetherto/wdk-wallet) accepts string | Uint8Array | ISigner. WalletManagerEvm's constructor accepts string | Uint8Array | ISignerEvm — stricter than the parent's contract, since ISignerEvm extends ISigner with extra required members (isDerivable, index, path, address, …).

That is a TypeScript subtyping violation:

error TS2345: Argument of type 'typeof WalletManagerEvm' is not assignable
              to parameter of type 'typeof WalletManager'.
  Types of parameters 'seedOrSigner' and 'signer' are incompatible.
    Type 'ISigner' is not assignable to type 'string | Uint8Array | ISignerEvm'.
      Type 'ISigner' is missing the following properties from type 'ISignerEvm':
        isDerivable, index, path, address, and 5 more.

which breaks wdk.registerWallet('ethereum', WalletManagerEvm, ...) (the standard consumer entry-point in @tetherto/wdk) under strict TypeScript. This is the second half of tetherto/wdk#72 — the getAccount half was already resolved by #40.

Fix

Widen the JSDoc @param type on the constructor from ISignerEvm to ISigner:

- * @param {string|Uint8Array|ISignerEvm} seedOrSigner - A BIP-39 seed phrase, seed bytes, or a root signer.
+ * @param {string|Uint8Array|ISigner} seedOrSigner - A BIP-39 seed phrase, seed bytes, or a root signer. Root signers must be derivable — non-derivable signers (e.g. private-key signers) can only be registered by name via `addSigner`.

Runtime behavior is unchanged: any signer whose isDerivable is falsy — which includes any plain ISigner without the EVM-specific extension — is already rejected by the existing if (!signer.isDerivable) guard. The widened type space does not admit any new successfully-constructed instances at runtime.

Scope

• src/wallet-manager-evm.js: @typedef import + @param change
• types/src/wallet-manager-evm.d.ts: surgically edited to mirror the source change; the rest of types/ is left as-is to avoid unrelated regeneration drift
• tests/wallet-manager-evm.test.js: 1 new test asserting a bare ISigner (no isDerivable) is rejected at construction

Test plan

• npm run lint — clean
• npm test — 111/111 (was 110; +1 for the new rejection test)
• npm run build:types — emits constructor(seedOrSigner: string | Uint8Array | ISigner, config?: EvmWalletConfig)
• Verified against wdk-core's docs TypeScript snippet: the constructor subtyping error is resolved

Marked as draft

Opening as draft since Issue #72 has an established history and I want to leave room for feedback on the description text and the additional test before it goes to review.