Add FluidStack provider boilerplate with comprehensive API stubs

[devin-ai-integration]

Implement cloud credential pattern for FluidStack provider

Summary

This PR implements the cloud credential pattern for the FluidStack provider to match the established Lambda Labs approach. The key change separates credential management from client operations by introducing a FluidStackCredential struct that implements the CloudCredential interface and creates FluidStackClient instances via MakeClient().

Key Changes:

• Added FluidStackCredential struct implementing CloudCredential interface with RefID/APIKey fields
• Updated FluidStackClient constructor to accept both refID and apiKey parameters (was previously just apiKey)
• Implemented tenant ID generation using SHA256 hash of API key with "fluidstack-" prefix
• Added capability delegation from credential to client via GetCapabilities() method
• Confirmed FluidStack image support from API documentation (supports image parameter with default "image://ubuntu22.04")

This addresses GitHub PR feedback from @theFong requesting the cloud credential pattern and clarification on image support.

Review & Testing Checklist for Human

• Verify interface compliance - Confirm both FluidStackCredential and FluidStackClient properly implement their respective interfaces by running go build ./internal/fluidstack/v1/... and checking for compilation errors
• Test credential -> client flow - Manually verify that NewFluidStackCredential().MakeClient() creates a working client and that GetReferenceID() returns the correct RefID
• Compare with Lambda Labs pattern - Side-by-side comparison of internal/fluidstack/v1/client.go vs internal/lambdalabs/v1/client.go to ensure structural consistency
• Verify GetCapabilities delegation - Test that FluidStackCredential.GetCapabilities() properly delegates to the client without circular dependencies or infinite loops
• Validate tenant ID generation - Confirm SHA256 hash generation produces consistent, non-empty tenant IDs for the same API key input

Recommended Test Plan: Create a FluidStackCredential instance, call MakeClient(), verify the resulting client has correct RefID, and test that GetCapabilities() works without errors.

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    subgraph "FluidStack Provider"
        FSClient["internal/fluidstack/v1/<br/>client.go"]:::major-edit
        FSCaps["internal/fluidstack/v1/<br/>capabilities.go"]:::context
        FSInstance["internal/fluidstack/v1/<br/>instance.go"]:::context
        FSInstanceType["internal/fluidstack/v1/<br/>instancetype.go"]:::context
    end

    subgraph "Core Interfaces"
        CloudCred["pkg/v1/client.go<br/>CloudCredential"]:::context
        CloudClient["pkg/v1/client.go<br/>CloudClient"]:::context
    end

    subgraph "Reference Pattern"
        LambdaClient["internal/lambdalabs/v1/<br/>client.go"]:::context
    end

    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit
        L3[Context/No Edit]:::context
    end

    FSClient -->|implements| CloudCred
    FSClient -->|implements| CloudClient
    FSClient -->|follows pattern| LambdaClient
    FSClient -->|delegates to| FSCaps

    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

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Notes

• Pattern Consistency: The implementation follows the exact Lambda Labs credential pattern established in the recent codebase updates
• Interface Risk: Both FluidStackCredential and FluidStackClient must implement complex interfaces - compilation success is necessary but manual verification of behavior is recommended
• Delegation Pattern: FluidStackCredential.GetCapabilities() creates a temporary client to fetch capabilities - this should be tested to ensure no circular dependencies
• Hash Consistency: Tenant ID generation uses the same SHA256 approach as Lambda Labs but should be verified for FluidStack-specific requirements

Session Details: Requested by Alec Fong (@theFong)
Link to Devin run: https://app.devin.ai/sessions/338c2a2ea6d34fd3ba76477ea88c47e6

[devin-ai-integration]

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[theFong]

remove all un-useful methods and files.

[theFong]

lets move this to the capabilities.go and remove the Project capabilities

[theFong]

please remove the unnecessary no implemented functions. Does fluidstack support images?

[theFong]

lets make a cloud cred that turns into a client. If you rebase lambda labs you will see how we implemented there.

[theFong]

lets make this a constant