Fix main thread encryption/decryption freeze

[0xFirekeeper]

A little slower for LocalWallet but better UX
Not doing this for EWS due to much heavier crypto operations that might take 10+ seconds to initial encryption, specially bad on mobile, best to do on main thread freeze 1-2s

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PR-Codex overview

The focus of this PR is to implement asynchronous operations in key generation and account unlocking processes.

Detailed summary

• Updated methods in Wallet.cs, ThirdwebLocalWallet.cs, and Utils.cs to use async and await for asynchronous operations.
• Replaced synchronous file operations with asynchronous operations for improved performance.
• Modified return types to Task or Task<string> for asynchronous handling.

✨ Ask PR-Codex anything about this PR by commenting with /codex {your question}

[github-actions]

Test Results for iOS

  1 files  ±0   15 suites  ±0   6m 56s ⏱️ -44s
 96 tests ±0   96 ✅ ±0  0 💤 ±0  0 ❌ ±0 
100 runs  ±0  100 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit b8979c2. ± Comparison against base commit 493f6ae.

[github-actions]

Test Results for WebGL

  1 files  ±0   15 suites  ±0   6m 46s ⏱️ -52s
 96 tests ±0   96 ✅ ±0  0 💤 ±0  0 ❌ ±0 
100 runs  ±0  100 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit b8979c2. ± Comparison against base commit 493f6ae.

[github-actions]

Test Results for Android

  1 files  ±0   15 suites  ±0   7m 6s ⏱️ -24s
 96 tests ±0   96 ✅ ±0  0 💤 ±0  0 ❌ ±0 
100 runs  ±0  100 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit b8979c2. ± Comparison against base commit 493f6ae.

[github-actions]

Test Results for StandaloneLinux64

  1 files  ±0   15 suites  ±0   7m 13s ⏱️ -14s
 96 tests ±0   96 ✅ ±0  0 💤 ±0  0 ❌ ±0 
100 runs  ±0  100 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit b8979c2. ± Comparison against base commit 493f6ae.