feat: anonymous adoption telemetry on first client.New

Sends one fire-and-forget POST per process the first time a consumer
constructs a Bot via client.New. Helps track real-world adoption and
version spread of the library. No identifiers, no API contents.

Implementation:
- new client/version.go: exported Version var (currently 0.7.11)
- new client/telemetry.go: sync.Once gate + telemetry.Send call
- client.go New(): single fireTelemetryOnce() line at function entry
- client/telemetry_test.go: TestMain disables outgoing pings during the
  library's own test suite

README §Telemetry documents the payload, the opt-out env vars, and links
to the upstream oss-telemetry source so consumers can audit what is sent.

Opt out via any of:
  DO_NOT_TRACK=1
  OSS_TELEMETRY_DISABLED=1
  GO_TELEGRAM_DISABLE_TELEMETRY=1
  osstelemetry.Disable() before the first client.New

client/telemetry.go

@@ -0,0 +1,33 @@
+package client
+
+import (
+	"sync"
+
+	telemetry "github.com/lukaszraczylo/oss-telemetry"
+)
+
+// telemetryOnce guards the single anonymous "library used" ping that is sent
+// on the first call to New. Long-running bots typically construct one Bot;
+// short-lived programs or test suites may construct many, but the Once gate
+// keeps the fire-and-forget call from amplifying into per-construction pings.
+var telemetryOnce sync.Once
+
+// fireTelemetryOnce dispatches a fire-and-forget anonymous adoption ping.
+//
+// The call is failproof by contract of oss-telemetry: it never blocks New,
+// never panics, never returns errors, and silently no-ops if disabled or
+// if the network is unavailable.
+//
+// Opt-out is honored via any of these environment variables (case-insensitive
+// truthy values "1", "true", "yes", "on"):
+//
+//   - DO_NOT_TRACK
+//   - OSS_TELEMETRY_DISABLED
+//   - GO_TELEGRAM_DISABLE_TELEMETRY
+//
+// See README §Telemetry for the full disclosure.
+func fireTelemetryOnce() {
+	telemetryOnce.Do(func() {
+		telemetry.Send("go-telegram", Version)
+	})
+}