[perf](trx-backend-soapysdr): reduce wfm resampler taps from 64 to 32

With Blackman-Harris window and proper cutoff (~0.24), 32 taps still
provides 60+ dB stopband rejection. Halves the per-sample MAC count
from 192 to 96 across the three resampler channels.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-server/trx-backend/trx-backend-soapysdr/src/demod.rs

@@ -41,7 +41,7 @@ const STEREO_MATRIX_GAIN: f32 = 0.50;
 /// and modulate higher-frequency stereo detail.
 const STEREO_DIFF_DC_R: f32 = 0.9995;
 /// Fractional-resampler FIR taps for WFM audio reconstruction.
-const WFM_RESAMP_TAPS: usize = 64;
+const WFM_RESAMP_TAPS: usize = 32;
 /// Polyphase slots for the WFM fractional FIR resampler.
 const WFM_RESAMP_PHASES: usize = 128;
 fn build_wfm_resample_bank(cutoff: f32) -> [[f32; WFM_RESAMP_TAPS]; WFM_RESAMP_PHASES] {