Add Fallback function

[ghosind]

For #6

[Copilot]

Pull Request Overview

This PR adds a fallback function pattern to the go-async library that tries functions in sequence until one succeeds. The implementation includes both context-aware and standard variants along with comprehensive tests and documentation.

• Adds Fallback and FallbackWithContext functions that execute functions sequentially until one succeeds
• Provides comprehensive test coverage including success, failure, and context scenarios
• Updates documentation to include the new fallback functionality

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
fallback.go	Core implementation of fallback functions with sequential execution logic
fallback_test.go	Comprehensive test suite covering success, failure, and context scenarios
README.md	Updated function list to include Fallback function
README-CN.md	Updated Chinese documentation with function list and missing note section

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.03%. Comparing base (40b4f2f) to head (e185c51).

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #7      +/-   ##
==========================================
+ Coverage   99.01%   99.03%   +0.02%     
==========================================
  Files          13       14       +1     
  Lines         710      725      +15     
==========================================
+ Hits          703      718      +15     
  Misses          6        6              
  Partials        1        1              

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