perf: reduce memory in to_python() (return PyList instead of Vec)

[dimastbk]

Partial fix #42. Return PyList instead of Vec - remove unnecessary reallocation.

Memory:
example file (saved as xlsx in LibreOffice).

Perormance:
A benchmark for reading files from https://github.com/MarkPflug/Benchmarks/tree/main/source/Benchmarks/Data using pandas.read_excel (first - all file, second - first 10 rows).

Before

[75.00%] ··· io.excel.ReadExcel.time_read_excel
[75.00%] ··· ========== ============ ============ ============ ============
             --                                 ext                        
             ---------- ---------------------------------------------------
               engine       xlsx         xlsm         xlsb         xls     
             ========== ============ ============ ============ ============
              calamine   1.29±0.01s   1.28±0.01s    821±4ms      816±7ms   
                None     6.62±0.01s   6.66±0.02s   4.83±0.01s   1.65±0.01s 
             ========== ============ ============ ============ ============

[100.00%] ··· io.excel.ReadExcelNRows.time_read_excel 
[100.00%] ··· ========== ============ ============ ========== =========
              --                              ext                      
              ---------- ----------------------------------------------
                engine       xlsx         xlsm        xlsb       xls   
              ========== ============ ============ ========== =========
               calamine    576±2ms      578±3ms     99.1±1ms   102±2ms 
                 None     16.8±0.6ms   16.4±0.6ms   61.6±2ms   1.04±0s 
              ========== ============ ============ ========== =========

After

[75.00%] ··· io.excel.ReadExcel.time_read_excel
[75.00%] ··· ========== ============ ============ ========== ============
             --                                ext                       
             ---------- -------------------------------------------------
               engine       xlsx         xlsm        xlsb        xls     
             ========== ============ ============ ========== ============
              calamine   1.23±0.01s    1.23±0s     760±10ms    753±3ms   
                None     6.60±0.02s   6.59±0.04s   4.66±0s    1.64±0.01s 
             ========== ============ ============ ========== ============

[100.00%] ··· io.excel.ReadExcelNRows.time_read_excel 
[100.00%] ··· ========== ============ ============ ========== =========
              --                              ext                      
              ---------- ----------------------------------------------
                engine       xlsx         xlsm        xlsb       xls   
              ========== ============ ============ ========== =========
               calamine    581±5ms      577±3ms     99.3±3ms   103±2ms 
                 None     17.7±0.3ms   17.5±0.5ms   61.4±2ms   1.04±0s 
              ========== ============ ============ ========== =========

[dimastbk]

Using PyTuple (black line) get more performance, but it's breaking changes for some cases..