Client: add DoContext method for context.Context-aware request execution

Feature Request

Is your feature request related to a problem? Please describe.

The fasthttp client provides DoTimeout() and DoDeadline(), but lacks a DoContext(ctx context.Context, req, resp) method. This means:

1. No cancellation propagation: If a parent context is cancelled (e.g., an HTTP handler's ctx.Done()), the in-flight fasthttp request continues until its own timeout or completion.
2. No deadline inheritance: If a caller has an existing context with a deadline (e.g., from gRPC or an upstream request), there's no way to pass it through.
3. No metadata attachment: Tracing systems (OpenTelemetry, etc.) rely on context to propagate trace IDs.

This forces users to either:

• Use net/http (which has Client.Do(req.WithContext(ctx))) and lose performance
• Manually create a context.WithTimeout and call DoDeadline, losing parent cancellation

Describe the solution you'd like

Add a DoContext method to both Client and HostClient:

func (c *Client) DoContext(ctx context.Context, req *Request, resp *Response) error
func (c *HostClient) DoContext(ctx context.Context, req *Request, resp *Response) error

Behavior:

• If ctx is already cancelled, return ctx.Err() immediately
• If ctx has a deadline, use it (respecting any existing timeout set on the Client)
• If the context is cancelled during dial, reading, or writing, abort the operation and return ctx.Err()
• The implementation can reuse the existing timeout/deadline logic in the TCP dialer, which already uses context.Context internally

Describe alternatives you've considered

• Using DoDeadline with ctx.Deadline() — works but loses cancellation propagation (only deadline is respected, not ctx.Done())
• Wrapping DoTimeout in a goroutine with select { case <-ctx.Done() } — racy, doesn't actually cancel the underlying I/O
• Using net/http — defeats the purpose of using fasthttp

Additional context

• The internal tcpdialer already uses context.Context for DNS resolution (Resolver.LookupIPAddr(ctx, host))
• Server.ShutdownWithContext(ctx) already exists, showing the project embraces context for lifecycle management
• Other Go HTTP clients (net/http, resty, go-resty) all support context-aware requests