fix(x/callback): audit remidiations

[spoo-bar]

Addressed + Added the following:

• When a callback is registered and after that the price of gas increases so much that the tx fees paid are not enough to cover the execution, the module would attempt to send extra amount to the fee collector and would panic. Fix ensures at max the txFees sent by the user are what is send to the fee collector
• isAuthorizedToModify func which was used to perform checks on who can create/update callbacks was case sensitive. The fix ensures even case insensitive inputs match
• Estimate callback fees would not error when input height was current height. Fix throws error when input height is in the past or the present
• Update ValidateBasic for MsgRegisterCallback to check the denom of the payment to be the sdk.DefaultBondDenom
• Modify the CancelCallback logic to prevent redundancy of logic in checking if the callback already exists
• Use prop values instead of getters at various places
• Some additional code comments
• Prevent blocked addresses from registering callbacks. During refund of callbacks, ensure the recipient is not blocked addr. If they are, send the amount to the fee collector instead. (Usually module accounts are blocked accounts. So they wont be creating callbacks. but added the checks to prevent panics and chain halts)

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (main@7e01661). Click here to learn what that means.

Files	Patch %	Lines
x/callback/types/msg.go	0.00%	5 Missing ⚠️
x/callback/keeper/keeper.go	0.00%	2 Missing and 1 partial ⚠️
x/callback/keeper/grpc_query.go	66.66%	1 Missing ⚠️
x/callback/keeper/msg_server.go	93.75%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #539   +/-   ##
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  Coverage        ?   64.62%           
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  Files           ?       88           
  Lines           ?     4851           
  Branches        ?        0           
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  Hits            ?     3135           
  Misses          ?     1550           
  Partials        ?      166           

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[fdymylja]

LGTM 🙏