Refactor and extend CPU channel model with float support

This commit refactors the CPU-based channel model for improved reusability and extends it with single-precision floating-point support.
This serves as a performance and correctness baseline for the new CUDA implementation.

Key changes include:

	- The original double-based multipath_channel function is refactored to remove hardcoded antenna dimensions from its signature. It now accepts dynamically sized arrays, making it more flexible for use in simulators like dlsim and ulsim.

	- A new multipath_channel_float function is introduced to operate on float data types, matching the GPU's native format.

	- A corresponding add_noise_float function is also added to complete the floating-point CPU pipeline.

	- The new float-based functions are designed to work with an interleaved IQ sample format ([I, Q, I, Q]), which is more suitable for vectorized (SSE) and GPU processing.

openair1/SIMULATION/TOOLS/sim.h

@@ -412,13 +412,39 @@ int random_channel(channel_desc_t *desc, uint8_t abstraction_flag);
 */
 
 void multipath_channel(channel_desc_t *desc,
-                       double *tx_sig_re[NB_ANTENNAS_TX],
-                       double *tx_sig_im[NB_ANTENNAS_TX],
-                       double *rx_sig_re[NB_ANTENNAS_RX],
-                       double *rx_sig_im[NB_ANTENNAS_RX],
+                       double **tx_sig_re,
+                       double **tx_sig_im,
+                       double **rx_sig_re,
+                       double **rx_sig_im,
                        uint32_t length,
                        uint8_t keep_channel,
 		       int log_channel);
+
+void multipath_channel_float(channel_desc_t *desc,
+                             float **tx_sig_interleaved,
+                             float **rx_sig_re,
+                             float **rx_sig_im,
+                             uint32_t length,
+                             uint8_t keep_channel,
+                             int log_channel);
+
+void interleave_channel_output(float **rx_sig_re,
+                               float **rx_sig_im,
+                               float **output_interleaved,
+                               int nb_rx,
+                               int num_samples);
+
+void add_noise_float(c16_t **rxdata,
+                     const float **r_re,
+                     const float **r_im,
+                     const float sigma2,
+                     const int length,
+                     const int slot_offset,
+                     const double ts,
+                     const int delay,
+                     bool apply_phase_noise,
+                     const uint8_t nb_antennas_rx);
+
 /*
 \fn double compute_pbch_sinr(channel_desc_t *desc,
                              channel_desc_t *desc_i1,