fix(account): rename deposit to add balance and add overflow check

[zcabter]

Context

This PR makes small changes to Account deposit mainly for consistency and safety:

• renames deposit to add_balance
• adds overflow check to add_balance

Description

Manually testing the PR

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 27.34%. Comparing base (6155f07) to head (8e6a2d8).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/jstz_proto/src/context/account.rs	83.33%	0 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
crates/jstz_proto/src/executor/deposit.rs	100.00% <100.00%> (ø)
crates/jstz_proto/src/context/account.rs	60.71% <83.33%> (+0.34%)	⬆️

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[johnyob]

lgtm 🚀 Fixes: https://app.asana.com/0/1205770721173533/1205832958749075/f