parity(storage): implement SetHeader method on storage client [from supabase-js]

[grdsdev]

SDK Parity: C# implementation needed

A change was made in supabase-js that needs to be implemented in this repository for SDK parity.

Reference Implementation (supabase-js)

• Commit: b1beee6
• PR: #2079
• Module: storage
• Type: new-feature

What Changed

A new public setHeader(name, value) method was added to BaseApiClient in storage-js. This allows setting per-request HTTP headers on storage operations.

Code Reference

public setHeader(name: string, value: string): this {
  this.headers = { ...this.headers, [name]: value }
  return this
}

Implementation Guidance

Expected API Surface (C#)

public StorageFileApi SetHeader(string name, string value)
{
    var newHeaders = new Dictionary<string, string>(Headers) { [name] = value };
    Headers = newHeaders;
    return this;
}

Key Behaviors to Match

• Creates a copy of headers to avoid mutating shared state
• Returns this for method chaining
• PascalCase naming per C# conventions

Acceptance Criteria

• SetHeader(name, value) method implemented on storage client
• Headers are copied (not mutated) when setting
• Method chaining supported
• Unit tests cover happy path and edge cases
• Documentation updated

Context

• supabase-js version: v2.95.3
• Parity tracking: This issue was auto-generated by SDK parity analysis
• Related parity issues: SDK-691 (dart), SDK-692 (py), SDK-693 (swift)

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Generated with Claude Code /sync-sdk-parity