Bug: Context getters have panics, silent overwrites, and inconsistent behavior

[odysseus0]

Summary

The rpcserver context helpers have two concrete issues:

1. Two functions panic on missing values
2. Inconsistent error-handling across getters

---

Bug 1: Panics

// jsonrpc_server.go:432 - PANICS if sizeKey not in context
func GetRequestSize(ctx context.Context) int {
    return ctx.Value(sizeKey{}).(int)
}

// jsonrpc_server.go:436 - PANICS if urlKey not in context  
func GetURL(ctx context.Context) *url.URL {
    return ctx.Value(urlKey{}).(*url.URL)
}

Call these outside a handler (e.g., in a test, a goroutine, or refactored code path) and they crash.

---

Bug 2: Inconsistent Contracts

Function	Missing Value Behavior
GetHighPriority	Returns false
GetSigner	Returns zero address
GetRequest	Returns nil
GetBuilderNetSentAt	Returns zero time
GetRequestSize	Panics
GetURL	Panics

Callers can't know which are safe without reading source.

---

Proposed Fix

Replace context.Value() getters with a typed wrapper (like Gin/Echo):

type RPCContext struct {
    Request     *http.Request  // guaranteed non-nil
    URL         *url.URL       // guaranteed non-nil  
    RequestSize int
    Signer      common.Address
    // ...
}

func (h *Handler) Method(rctx *RPCContext, args Args) (Result, error) {
    rctx.Request.Header.Get("X-Foo")  // always safe
}

No panics, no magic keys, explicit contracts.

---

Why Now

Hit this adding header logging across services. Every call site needed nil checks or risked panics. The current design makes simple tasks error-prone.