perf(dispatch): typed Context.Command/CommandArgs/RegexMatch fields

Move the three conventional Values keys ("command", "command_args", "regex_match") to typed fields on Context. Router and group routing write the fields directly; the Values map is allocated lazily via the new Set method and reserved for user-defined custom keys.

Allocation impact (M4 Max, b.Loop()):

  DispatchCommand:   5 allocs/op -> 1, 153ns -> 69ns (-55%)

  DispatchTextRegex: 5 allocs/op -> 2, 181ns -> 107ns (-41%)

  DispatchFilter:    2 allocs/op -> 1, 32ns -> 19ns (-41%)

  NewContext:        5.79ns -> 1.60ns

Trade-off: Context struct grew from ~48B to ~96B (three new fields), so filter-only paths pay ~50B more per dispatch. Command/regex paths save ~320B + 4 allocs each, which dominates for typical bot workloads.

Handlers reading c.Values["command"], c.Values["command_args"], or c.Values["regex_match"] now get nil; the typed fields c.Command, c.CommandArgs, c.RegexMatch are the new accessors. Custom keys still work via c.Set(k, v) and c.Values[k].

dispatch/router_test.go

@@ -52,7 +52,7 @@ func TestRouter_OnCommandMatches(t *testing.T) {
 	r := New(b)
 	hit := make(chan string, 1)
 	r.OnCommand("/start", func(c *Context, m *api.Message) error {
-		hit <- c.Values["command"].(string)
+		hit <- c.Command
 		return nil
 	})
 
@@ -82,7 +82,7 @@ func TestRouter_OnText(t *testing.T) {
 	r := New(client.New("t"))
 	hit := make(chan []string, 1)
 	r.OnText(`^hello (\w+)$`, func(c *Context, m *api.Message) error {
-		hit <- c.Values["regex_match"].([]string)
+		hit <- c.RegexMatch
 		return nil
 	})
 
@@ -164,10 +164,7 @@ func TestRouter_NonASCIICommand(t *testing.T) {
 	r := New(client.New("t"))
 	hit := make(chan [2]string, 1)
 	r.OnCommand("/старт", func(c *Context, m *api.Message) error {
-		hit <- [2]string{
-			c.Values["command"].(string),
-			c.Values["command_args"].(string),
-		}
+		hit <- [2]string{c.Command, c.CommandArgs}
 		return nil
 	})
 
@@ -180,16 +177,15 @@ func TestRouter_NonASCIICommand(t *testing.T) {
 	require.Equal(t, "аргумент", got[1])
 }
 
-// TestRouter_CommandValuesNotLeakedOnNoMatch verifies that c.Values["command"]
-// is not set when a command entity is present but no route matches, so a
+// TestRouter_CommandValuesNotLeakedOnNoMatch verifies that c.Command is
+// empty when a command entity is present but no route matches, so a
 // subsequent text handler doesn't see stale values.
 func TestRouter_CommandValuesNotLeakedOnNoMatch(t *testing.T) {
 	r := New(client.New("t"))
 	// Register a text handler that should fire as fallback.
 	leaked := make(chan bool, 1)
 	r.OnText(`.*`, func(c *Context, m *api.Message) error {
-		_, hasCmd := c.Values["command"]
-		leaked <- hasCmd
+		leaked <- c.Command != ""
 		return nil
 	})
 	// No OnCommand registered, so the command entity won't match any route.