`subset.py`: support `--lat/lon` in radar coordinates (#1238)

+ `coord.geo2radar()`: use smaller search range (x/y_factor) for more accurate conversion. Tests based on Sentinel-1 miaplpy dataset show this change brings the conversion accuracy to the sub-pixel level.

+ `subset`: support subsetting radar-coded files using lat/lon
   - revert the change in `subset_input_dict2box()` to remain its simplicity as described in the comment.
   - `read_aux_subset2inps()`: add the code body to convert bbox in lat/lon to bbox in y/x for radar-coded files
   - `read_aux_subset2inps()`: set `buf=0` while calling `bbox_geo2radar()` for a more precise conversion, the extra buffer zone seems not needed, as it already produces a slightly bigger bbox during the geo2radar conversion, even with buf=0.

+ `cli/subset`: add usage example for radar-coded files

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Co-authored-by: Zhang Yunjun <yunjunz@outlook.com>