add fallback support for `ChainReader` on `AvsReader`

[JulianVentura]

We should add a ChainReaderFallback inside AvsReader, so we can tolerate RPC node failure, like so:

type AvsReader struct {
	ChainReader *sdkavsregistry.ChainReader
	ChainReaderFallback *sdkavsregistry.ChainReader
	AvsContractBindings            *AvsServiceBindings
	AlignedLayerServiceManagerAddr ethcommon.Address
	logger                         logging.Logger
}

then, refactor the functions which make use of it to add the fallback call in case of failure.