fix: pass undefined instead of empty object for signOptions in ChainWalletStore

[faneaatiku]

Fix ChainWalletStore.getOfflineSigner() passing {} instead of undefined as signOptions to cosmosWallet.signAmino() and cosmosWallet.signDirect().

Problem
CosmosWallet in core defines defaultSignOptions = { preferNoSetFee: true } and applies them via signOptions || this.defaultSignOptions. Since {} is truthy, the fallback never triggers and the defaults are silently dropped.

Without preferNoSetFee: true, Keplr overrides the application-provided fee with its own calculation using the chain's native denom. This breaks any app that pays fees in a non-native denomination.

Fix
Pass undefined instead of {} for both signAmino and signDirect so the defaults in core are respected.

[devin-ai-integration]

Thanks for this fix — and sorry for the long wait. The change itself is correct: CosmosWallet.signAmino/signDirect fall back with signOptions || this.defaultSignOptions, so a truthy {} silently drops preferNoSetFee: true and Keplr overrides the app's fee. Passing undefined restores the defaults. I also grepped for other {} signOptions call sites; the only other one is wallets/ledger/src/cosmos.ts, which is Ledger's own signer and not affected.

One blocker: two existing unit tests still assert the old {} argument, so pnpm test fails on this branch (merged onto current main; main itself is green):

packages/store test: ● ChainWalletStore › Offline Signer › should handle signAmino calls
packages/store test: ● ChainWalletStore › Offline Signer › should handle signDirect calls
    - Expected  {}
    + Received  undefined

Fix: in packages/store/__tests__/chain-wallet-store.test.ts, change the 4th expected argument of both toHaveBeenCalledWith(...) assertions from {} to undefined. With that change the full suite passes (store: 176/176). A ready-made version of that 2-line test update is on branch devin/1790884011-pr42-fixup (commit ea669dc) if the maintainers prefer to land it alongside this PR.

Non-blocking follow-up idea for maintainers: making CosmosWallet merge options ({ ...this.defaultSignOptions, ...signOptions }) instead of || would stop any caller from accidentally dropping the defaults by passing a partial object.

Reviewed by Devin on behalf of @pyramation

[devin-ai-integration]

Correction to the review above: the ready-made test fix now lives in #46 (branch fix/pr42-sign-options-tests, this PR's commit + the 2-line assertion update). Either land this PR with the assertions changed to undefined, or merge #46 — same result.