fix: extend Safe wallet provider tests

[iamacook]

What it solves

Extends test coverage of SafeWalletProvider and useSafeWalletProvider

How this PR fixes it

All explicit methods of SafeWalletProvider and useSafeWalletProvider are now covered by unit tests.

How to test it

Observe the tests for SafeWalletProvider and useSafeWalletProvider passing.

Checklist

• I've tested the branch on mobile 📱
• I've documented how it affects the analytics (if at all) 📊
• I've written a unit/e2e test for it (if applicable) 🧑‍💻

[github-actions]

Branch preview

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https://safe_wallet_provider_tests--walletweb.review-wallet-web.5afe.dev

[github-actions]

ESLint Summary View Full Report

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Type	Occurrences	Fixable
Errors	0	0
Warnings	0	0
Ignored	0	N/A

• Result: ✅ success
• Annotations: 0 total

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^{Report generated by eslint-plus-action}

[iamacook]

As these are just tests, I'm going to merge them directly.