imp(staking): change the validator address in the events from string type to address type

[luchenqun]

Description

In #2030, you recommend use address instead of string for validator address in events. I think this is a good idea. Using address instead of string would make it easier for developers to track the corresponding validator, because use string type the recorded value would be keccak256(validatorAddress). Moreover, it would be difficult to decode events and determine which validator the hash corresponds to if string type is used. Therefore, I have updated the string type validator address in other events to address type.

Here is an example of a Delegate event before and after the update

Before Delegate event with validator address as string
keeack256("evmosvaloper1hajh6rhhkjqkwet6wqld3lgx8ur4y3khljfx82")
-->
"0xc30b39324ec8e945bd2d238ee3e5475a8108e9d0c37e1278c4b0ec30283fdacf"

Afte Delegate event with validator address as address type
bech32 "evmosvaloper1hajh6rhhkjqkwet6wqld3lgx8ur4y3khljfx82"
<-->
hex "0xbf657D0ef7b48167657A703Ed8Fd063F075246D7"

[codecov]

Codecov Report

Merging #2053 (6b0ad92) into main (e51d4d6) will increase coverage by 0.01%.
Report is 3 commits behind head on main.
The diff coverage is 43.47%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2053      +/-   ##
==========================================
+ Coverage   70.16%   70.18%   +0.01%     
==========================================
  Files         340      340              
  Lines       25448    25443       -5     
==========================================
+ Hits        17856    17857       +1     
+ Misses       6679     6669      -10     
- Partials      913      917       +4     

Files	Coverage Δ
precompiles/staking/types.go	74.76% <ø> (ø)
precompiles/staking/events.go	63.30% <43.47%> (+1.86%)	⬆️

[fedekunze]

Thanks for the contribution! Looks good to me. There's a minor issue with the formatting