test(token-vesting): strong error types, explicit checks in tests, and deregister tests

[Unique-Divine]

• Closes test(vesting): deregister code path needs unit tests #82

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• ci: Exclude prost types from nibiru-std/src/proto/buf from coverage + fmt
• feat(nibiru-std): implement NibiruStargateQuery as an extension of prost::Nme
• test(nibiru-std): verify that CosmosMsg::Stargate types error when converted to QueryRequest::Stargate
• test(token-vesting): add tests for execute deregister
• test(token-vesting): clean up linear vesting tests
• test(token-vesting): use strongly-typed, idiomatic errors
• test(token-vesting): use typed errors + Result types in contract.rs
• test(token-vesting): use explicit error comparisons in tests + Result types in testing.rs

[codecov]

Codecov Report

Attention: 21 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
contracts/token-vesting/src/errors.rs	100.00% <100.00%> (ø)
contracts/token-vesting/src/contract.rs	96.51% <96.12%> (+22.55%)	⬆️
contracts/token-vesting/src/msg.rs	88.76% <88.23%> (-1.62%)	⬇️
contracts/token-vesting/src/testing.rs	98.89% <96.31%> (-0.06%)	⬇️

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