feat: Add DecodeRTPEndBit for DTMF decoding without Marker bit requirement

[usluio]

Summary

Adds DecodeRTPEndBit, an alternative DTMF RTP decoding function that uses the RFC 4733 End bit instead of the Marker bit to determine event completion.

Problem

The existing DecodeRTP requires the RTP Marker bit to be set on incoming DTMF packets. Many SIP providers/gateways do not consistently set the Marker bit (RFC 4733 §2.3.1), causing DTMF events to be silently dropped.

Solution

Added DecodeRTPEndBit as an alternative decoding mode:

func DecodeRTPEndBit(h *rtp.Header, payload []byte) (Event, bool)

[usluio]

:) @dennwc thx

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[biglittlebigben]

I will defer to the telephony team for feedback on the core of the patch, bur please cleanup the imports before we can consider this.

[usluio]

I will defer to the telephony team for feedback on the core of the patch, bur please cleanup the imports before we can consider this.

Resolved