feat: add region as forceFunctionRegion query parameter

[grdsdev]

Summary

This PR ports the region functionality from functions-js PR #100 to the Flutter/Dart implementation.

Changes

• FunctionsClient: Added optional region parameter to constructor and invoke() method
• Region handling: When region is specified and not 'any':
  • Adds x-region header to the request
  • Adds forceFunctionRegion query parameter to the URL
• SupabaseClient: Added FunctionsClientOptions to configure default region
• Tests: Added comprehensive test coverage for region functionality

Features

• Region can be set at client level (constructor) or per-invocation (invoke method)
• Per-invocation region overrides client-level region
• Region value 'any' is treated as no region preference
• Maintains backward compatibility - all existing code continues to work

Usage Examples

// Set region at client level
final client = FunctionsClient(
  url,
  headers,
  region: 'us-west-1',
);

// Or set region per invocation
await client.invoke('my-function', region: 'eu-west-1');

// Via SupabaseClient
final supabase = SupabaseClient(
  url,
  anonKey,
  functionsOptions: FunctionsClientOptions(region: 'us-east-1'),
);

Test plan

• All existing tests pass
• Added new tests for region functionality:
  • Region parameter adds both header and query parameter
  • Region 'any' does not add header or query parameter
  • Client region is used when invoke region is not specified
  • Invoke region overrides client region
  • Region works with other query parameters
• Code passes dart analyze with no warnings
• Code formatted with dart format

🤖 Generated with Claude Code

[coveralls]

Pull Request Test Coverage Report for Build 18144638702

Details

• 14 of 14 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.05%) to 80.646%

---

Totals
Change from base Build 18131530215:	0.05%
Covered Lines:	3146
Relevant Lines:	3901

---

💛 - Coveralls