ERC721_TotalSupply Include Burned NFTs

[0xFirekeeper]

Closes #109

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PR-Codex overview

This PR updates the ERC721_TotalSupply method in the ThirdwebExtensions class to improve error handling and change the logic for retrieving the total supply of tokens.

Detailed summary

• Changed the null check for contract to an if statement with a throw.
• Added a try-catch block to attempt reading nextTokenIdToMint.
• In case of an exception, it falls back to reading totalSupply.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 78.00%. Comparing base (79f6f92) to head (b971fa5).

Files with missing lines	Patch %	Lines
Thirdweb/Thirdweb.Extensions/ThirdwebExtensions.cs	25.00%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #112      +/-   ##
==========================================
- Coverage   78.01%   78.00%   -0.01%     
==========================================
  Files          28       28              
  Lines        4698     4705       +7     
  Branches      639      639              
==========================================
+ Hits         3665     3670       +5     
- Misses        859      861       +2     
  Partials      174      174              

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