Support for 1.25MHz capture (#1418)

* Advanced draft decim /4 just waterfall ok

* apply some Kall's corrections + formatting

* Tidy up both decim_factors

* New refine optimizations

* Format issues

* more format issues ...mmmm

* comments update

* WIP Cleanup

* WIP

* WIP - add variant

* Use std::visit to dispatch MultiDecimator -- fluent API

* Clean up comments

* Merge next and fix compilation

* Fix odd loop in BlockDecimator

* Clean up spectrum math

* Descibe spectrum update math better, more clear math.

* Apply spectrum interval correction at 1.5M

* Increase replay buffer to handle x4 ovs

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Co-authored-by: Brumi-2021 <ea3hqj@gmail.com>

firmware/baseband/dsp_decimate.cpp

@@ -202,8 +202,8 @@ buffer_c16_t FIRC8xR16x24FS4Decim4::execute(
     uint32_t* const d = static_cast<uint32_t*>(__builtin_assume_aligned(dst.p, 4));
 
     const auto k = output_scale;
-
     const size_t count = src.count / decimation_factor;
+
     for (size_t i = 0; i < count; i++) {
         const vec4_s8* const in = static_cast<const vec4_s8*>(__builtin_assume_aligned(&src.p[i * decimation_factor], 4));