fix(bigtable): Track number of rows read to set rowsLimit in subsequent requests

[bhshkh]

Tracking bug: b/303943537

This PR fixes TestReadRows_NoRetry_ErrorAfterLastRow test

https://github.com/googleapis/cloud-bigtable-clients-test/blob/db4d6a9e8e5e38b6f07383bd46ac14bfc8d8b9b6/tests/readrows_test.go#L171-L173

fails with error:

--- FAIL: TestReadRows_NoRetry_ErrorAfterLastRow (0.03s)
    readrows_test.go:201: 
        	Error Trace:	cloud-bigtable-clients-test/tests/readrows_test.go:201
        	Error:      	Not equal: 
        	            	expected: 1
        	            	actual  : 2
        	Test:       	TestReadRows_NoRetry_ErrorAfterLastRow
--- FAIL: TestReadRows_Retry_LastScannedRow_Reverse (0.04s)

The test sends below request to Go Bigtable proxy:

Request: &btpb.ReadRowsRequest{
	TableName: buildTableName("table"),
	RowsLimit: 1,
},

On receiving the request, the proxy creates a ReadRows request for the client library and invokes ReadRows function.
Even though test sends RowsLimit field in the method, the proxy does not add it to the client library request. This has been fixed in this PR.

[codyoss]

@bhshkh is this still wanted/needed?

[bhshkh]

@bhshkh is this still wanted/needed?

Yes