blocks/sources/sdrplay: add SDRplay startup options

[bjkramp76]

This updates SDRplaySource startup-time configuration and fixes bandwidth handling.

Summary:

• Fix the documented bandwidth option so it is actually applied to tunerParams.bwType in the newer libsdrplay_api path.
• Fix exact SDRplay bandwidth matching so exact supported values select themselves instead of the next lower bandwidth.
• Add RSPduo physical input selection via rspduo_input:
  • tuner1_50ohm
  • tuner1_hiz
  • tuner2_50ohm
• Select RSPduo Tuner B before sdrplay_api_SelectDevice() when tuner2_50ohm is requested.
• Use the active rxChannelA / rxChannelB for tuner parameters instead of hard-coding rxChannelA.
• Register both Stream A and Stream B callbacks for RSPduo so Tuner B works correctly.
• Re-apply RSPduo AM-port selection after sdrplay_api_Init() so Tuner 1 Hi-Z / 50-ohm selection takes effect.
• Add guarded startup options for RSP1A, RSP2, RSPduo, and RSPdx where matching SDRplay API fields are already declared.
• Reject unsupported model-specific options instead of silently ignoring them.

Hardware tested with an RSPduo:

• AM broadcast band on Tuner 1 Hi-Z
• WBFM on Tuner 1 50-ohm
• WBFM on Tuner 2 50-ohm
• APRS / AX.25 reception on 144.390 MHz using Tuner 1 50-ohm

Notes:

• The RSPduo paths above were hardware-tested.
• The RSP1A, RSP2, and RSPdx options are API-mapped and model-guarded, but I do not have those devices for bench testing.
• Runtime retuning, soft-stop files, and GUI polling/control-file logic are intentionally not included here. This PR only changes startup-time SDRplaySource configuration.