Add go-llm v2: redesigned API for simpler LLM abstraction

v2 is a new Go module (v2/) with a dramatically simpler API:
- Unified Message type (no more Input marker interface)
- Define[T] for ergonomic tool creation with standard context.Context
- Chat session with automatic tool-call loop (agent loop)
- Streaming via pull-based StreamReader
- MCP one-call connect (MCPStdioServer, MCPHTTPServer, MCPSSEServer)
- Middleware support (logging, retry, timeout, usage tracking)
- Decoupled JSON Schema (map[string]any, no provider coupling)
- Sample tools: WebSearch, Browser, Exec, ReadFile, WriteFile, HTTP
- Providers: OpenAI, Anthropic, Google (all with streaming)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

v2/request.go

@@ -0,0 +1,37 @@
+package llm
+
+// RequestOption configures a single completion request.
+type RequestOption func(*requestConfig)
+
+type requestConfig struct {
+	tools       *ToolBox
+	temperature *float64
+	maxTokens   *int
+	topP        *float64
+	stop        []string
+}
+
+// WithTools attaches a toolbox to the request.
+func WithTools(tb *ToolBox) RequestOption {
+	return func(c *requestConfig) { c.tools = tb }
+}
+
+// WithTemperature sets the sampling temperature.
+func WithTemperature(t float64) RequestOption {
+	return func(c *requestConfig) { c.temperature = &t }
+}
+
+// WithMaxTokens sets the maximum number of tokens to generate.
+func WithMaxTokens(n int) RequestOption {
+	return func(c *requestConfig) { c.maxTokens = &n }
+}
+
+// WithTopP sets the nucleus sampling parameter.
+func WithTopP(p float64) RequestOption {
+	return func(c *requestConfig) { c.topP = &p }
+}
+
+// WithStop sets stop sequences.
+func WithStop(sequences ...string) RequestOption {
+	return func(c *requestConfig) { c.stop = sequences }
+}