Added modifier to remove duplication

[Upendra-Jaiswal]

Description

the hasSufficientFunds modifier is defined at the top of the contract. This modifier checks if the caller has sufficient funds to perform the requested operation, and if not, it will throw an error.

The withdraw and transferAmt functions both use the hasSufficientFunds modifier, which means that they will both check if the caller has sufficient funds before executing any other code in the function. This avoids repeating the same code in multiple places.

Fixes #144

Screenshots of relevant screens

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[github-actions]

PR is not linked to any issue, please make the corresponding changes in the body.

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PR is not linked to any issue, please make the corresponding changes in the body.

[Atharv181]

LGTM