Add server URL normalization for flexible WithServerURL input

[chris-freeman-glean]

Summary

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

Go-specific implementation

Uses Speakeasy's SDKInit hook mechanism (internal/hooks/server_url_normalizer.go). 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 Go SDK passes raw strings to the SDKInit hook.

The hook is registered in registration.go 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:
client := glean.New(glean.WithServerURL("mycompany-be.glean.com"))
client := glean.New(glean.WithServerURL("https://mycompany-be.glean.com"))
client := glean.New(glean.WithServerURL("https://mycompany-be.glean.com/"))

Backwards compatibility

The WithInstance() option continues to work unchanged. No breaking changes.

Test plan

• 7 table-driven tests pass covering normalization logic and hook integration