Update writeContracts and sendCalls return types and meaning (#4683)

* Update `writeContracts` and `sendCalls` return types and meaning

* docs: tweaks

---------

Co-authored-by: Tom Meagher <[email protected]>

Author: agsola

site/core/api/actions/sendCalls.md

@@ -206,9 +206,9 @@ const id = await sendCalls(config, {
 import { type SendCallsReturnType } from '@wagmi/core'
 ```
 
-`bigint`
+`{ id: string; capabilities?: WalletCapabilities | undefined }`
 
-Most recent block number seen.
+Identifier of the call batch.
 
 ## Error
 

site/core/api/actions/writeContracts.md

@@ -300,9 +300,9 @@ const id = await writeContracts(config, {
 import { type WriteContractsReturnType } from '@wagmi/core/experimental'
 ```
 
-`bigint`
+`{ id: string; capabilities?: WalletCapabilities | undefined }`
 
-Most recent block number seen.
+Identifier of the call batch.
 
 ## Error