Add profile system for S3-compatible endpoints

[vertix]

Summary

• Add profile system enabling access to multiple S3-compatible endpoints (MinIO, Nebius, etc.) simultaneously
• Support anonymous/public bucket access via public=True parameter
• Profiles can be registered by name or used inline as Profile objects
• Add default_profile parameter to mirror() context manager

Example

import pos3

pos3.register_profile('nebius-public',
    endpoint='https://storage.eu-north1.nebius.cloud',
    public=True
)

with pos3.mirror():
    # Download from Nebius public bucket
    dataset = pos3.download('s3://public-data/dataset/', profile='nebius-public')
    
    # Upload to AWS (default credentials)
    results = pos3.upload('s3://my-bucket/results/')

Test plan

• All existing tests pass
• Added 9 new tests for profile functionality
• Verified with real Nebius public bucket access

[vertix]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: e3717cc6d5

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[vertix]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: f4aa045fa8

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[vertix]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: e56deae2a8

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[vertix]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🎉

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".