fix(provider): list substates (#131)

Description
---
Fix `listSubstates` args. Should use bigint from number or null.

Motivation and Context
---
Error occurs if TU Provider calls `listSubstate` function with null for
`limit` or `offset`

How Has This Been Tested?
---
Manually tested with TU templates.

What process can a PR reviewer use to test or verify this change?
---
Pull this branch, build and use locally with any template which uses
`lisSubstates`

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Breaking Changes
---

- [x] None
- [ ] Requires data directory on base node to be deleted
- [ ] Requires hard fork
- [ ] Other - Please specify

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src/provider/TariUniverseProvider.ts

@@ -192,8 +192,8 @@ export class WalletDaemonTariProvider implements TariProvider {
     const res = await this.client.substatesList({
       filter_by_template,
       filter_by_type,
-      limit: BigInt(limit ?? 0),
-      offset: BigInt(offset ?? 0),
+      limit: limit ? BigInt(limit) : null,
+      offset: offset ? BigInt(offset) : null,
     })
     const substates = res.substates.map((s) => ({
       substate_id: substateIdToString(s.substate_id),