Add raw IQ replay and live IQ capture support

[vk5zsn]

Summary

This PR adds a minimal raw-IQ workflow on top of main:

• replay generic raw IQ captures through LTESniffer
• support raw cf32 and raw sc16 offline input
• add a live raw-IQ sink while decoding
• preserve compatibility with synchronized replay files from the LTESniffer-record-subframe branch
• make the offline DL DCI SNR gate configurable

User-visible changes

• -j
  Treat -i as a generic raw IQ capture and synchronize it before decoding.
• -J
  Interpret raw -i -j input as interleaved sc16 instead of cf32.
• -Q /path/to/output.bin
  In live RF mode, write the received IQ stream to a raw cf32 file while decoding.
• -G <dB>
  Minimum DL DCI search SNR for offline replay.

Implementation

• Added a file-backed receive callback so a raw file can be processed through ue_sync like a live RF source.
• Added optional sc16 -> cf_t conversion in the raw replay path.
• Added live receive-path IQ mirroring plus overflow / timestamp-gap summary reporting.
• Set offline replay PHICH resources to SRSRAN_PHICH_R_1 for compatibility with synchronized replay files.

Verification

Verified on a Raspberry Pi 5 with a B210.

Record-subframe replay

• replayed /home/vk2tlq/subframe_iq_sample.bin
• valid MIB decode
• nonzero offline decode stats

Direct raw cf32 replay

• replayed /home/vk2tlq/live_gold_763M_11p52M_cf32.bin with -j
• locked and decoded successfully
• nonzero DCI / location stats

Direct raw sc16 replay

• replayed /dev/shm/iq_763M_11p52M_sc16.bin with -j -J
• locked and decoded successfully
• nonzero DCI / location stats

Additional notes and local file manifests are included under docs/.