fix!: fix json-rpc failures for pruned nodes

[yihuang]

Closes: #1123
Solution:

• try to parse base fee from events if grpc query failed
• use a nil base fee if both grpc query and event parsing failed
• use zero address if query validator address failed
• optimize some json-rpc apis by the way.

Description

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[crypto-facs]

Everything LGTM besides my comment! 🚀

[fedekunze]

utACK