Add server URL normalization for flexible server_url input

[chris-freeman-glean]

Summary

Adds server URL normalization so users can pass schemeless URLs (e.g., "mycompany-be.glean.com") as server_url when constructing the SDK client. This is part of promoting server_url as the primary configuration option, replacing instance in all documentation and examples.

Python-specific implementation

Uses Speakeasy's SDKInit hook mechanism (src/glean/api_client/_hooks/server_url_normalizer.py). The hook receives the raw server URL string during SDK initialization and normalizes it before it's used for requests. This is the standard approach — the Python SDK passes raw strings to the SDKInit hook (unlike TypeScript which passes parsed URL objects).

The hook is registered in registration.py as the first hook to run during initialization.

Normalization rules

• No scheme → prepend https://
• http:// preserved (for localhost/dev)
• https:// preserved
• Trailing slashes stripped

User-facing API

# All of these now work identically:
glean = Glean(server_url="mycompany-be.glean.com")
glean = Glean(server_url="https://mycompany-be.glean.com")
glean = Glean(server_url="https://mycompany-be.glean.com/")

Backwards compatibility

The instance parameter continues to work unchanged. No breaking changes.

Test plan

• 13 unit tests pass covering normalization logic and hook integration