Contract: Add typed InvalidWasmHash error variant

[wheval]

Contract: Add typed InvalidWasmHash error variant

Description:
Upgrade hash validation needs a dedicated error for clear client handling.

Context:
Typed error improves observability and SDK mapping.

Requirements:

• Add InvalidWasmHash to ContractError
• Use it when upgrade hash input is invalid
• Add/update test assertions accordingly

Files to Modify:

• contracts/account/src/lib.rs

Definition of Done:

• Implementation is complete for this single task
• Contract tests updated or added where needed
• Existing contract tests remain green

Labels: security, Stellar Wave
Estimated Effort: 1 day
Priority: Low

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[uzochukwuV]

@uzochukwuV has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I would love to work on this issue, can you please assign it to me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @uzochukwuV to this issue.