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

---------

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

firmware/baseband/block_decimator.hpp

@@ -69,29 +69,22 @@ class BlockDecimator {
 
         set_input_sampling_rate(src.sampling_rate);
 
-        while (src_i < src.count) {
+        for (size_t src_i = 0; src_i < src.count; src_i += factor()) {
             buffer[dst_i++] = src.p[src_i];
             if (dst_i == buffer.size()) {
                 callback({buffer.data(), buffer.size(), output_sampling_rate()});
                 reset_state();
-                dst_i = 0;
             }
-
-            src_i += factor();
         }
-
-        src_i -= src.count;
     }
 
    private:
     std::array<T, N> buffer{};
     uint32_t input_sampling_rate_{0};
     size_t factor_{1};
-    size_t src_i{0};
     size_t dst_i{0};
 
     void reset_state() {
-        src_i = 0;
         dst_i = 0;
     }
 };