feat: add overrideHost/Port/Scheme to presigned URL methods

[hammadparveez]

Summary

Closes #101

In multi-network setups the MinIO client connects to an internal endpoint (e.g. http://internal-minio:9000), but presigned URLs distributed to external users must point to the public-facing address. Previously there was no way to customise the host/port/scheme of a presigned URL without instantiating a separate Minio client.

This PR adds three optional named parameters to presignedUrl(), presignedGetObject(), and presignedPutObject():

Parameter	Type	Description
overrideHost	String?	Replace the host in the presigned URL
overridePort	int?	Replace the port in the presigned URL
overrideScheme	String?	Replace the scheme (http/https)

All three are independent and optional — omitting one keeps the value from the client configuration. When any override is present, both the URL and the host header are updated before signing, so the resulting URL is fully valid for the external endpoint.

Usage example

final minio = Minio(
  endPoint: 'internal-minio.corp',
  port: 9000,
  useSSL: false,
  accessKey: '...',
  secretKey: '...',
);

// Generate a URL accessible from the public internet
final url = await minio.presignedGetObject(
  'my-bucket',
  'my-object.jpg',
  overrideHost: 'storage.example.com',
  overridePort: 443,
  overrideScheme: 'https',
);

Changes

• lib/src/minio.dart — added parameters to presignedUrl, presignedGetObject, presignedPutObject
• test/minio_presigned_url_test.dart — 6 new unit tests covering each override param and combined usage

Test plan

• All existing presigned URL tests pass
• New tests verify overrideHost, overridePort, overrideScheme individually and combined for both GET and PUT
• Manual test: generate a presigned URL with overrides and verify it resolves via the public endpoint

[Copilot]

Pull request overview

Adds the ability to override the host/port/scheme used when generating presigned URLs so that a client can talk to an internal MinIO endpoint while distributing externally-valid presigned URLs.

Changes:

• Add optional overrideHost, overridePort, and overrideScheme named parameters to presignedUrl(), presignedGetObject(), and presignedPutObject().
• Apply URL + Host header overrides prior to SigV4 presigning.
• Extend presigned URL unit tests to assert URL components reflect overrides.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
lib/src/minio.dart	Adds override parameters and rewrites the request URL/host header before calling SigV4 presign logic.
test/minio_presigned_url_test.dart	Adds tests asserting the generated presigned URL reflects override host/port/scheme.

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