whenxuan: move the data generator to utils

Author: wwhenxuan

README.md

@@ -145,7 +145,8 @@ plot_IMFs(signal, IMFs)             # per-channel panels
 | [`SJMD`](https://github.com/wwhenxuan/PySDKit/blob/main/pysdkit/_jmd/sjmd.py) / `SMJMD` (Successive Jump and Mode Decomposition) |         [[paper]](https://arxiv.org/abs/2504.08453)          |                          [[code]]()                          | [[notebook]](https://github.com/wwhenxuan/PySDKit/blob/main/examples/jmd/sjmd.ipynb) |
 | [`ESMD`](https://github.com/wwhenxuan/PySDKit/blob/main/pysdkit/_emd/esmd.py) (Extreme-Point Symmetric Mode Decomposition) |          [[paper]](https://arxiv.org/abs/1303.6540)          |         [[code]](https://github.com/WuShichao/esmd)          | [[notebook]](https://github.com/wwhenxuan/PySDKit/blob/main/examples/emd_variants/esmd.ipynb) |
 | [`STNBMD`](https://github.com/wwhenxuan/PySDKit/blob/main/pysdkit/_vncmd/stnbmd.py) (Short-Time Narrow-Band Mode Decomposition) | [[paper]](https://www.sciencedirect.com/science/article/pii/S0022460X16002443?via%3Dihub) | [[code]](https://ww2.mathworks.cn/matlabcentral/fileexchange/56226-short-time-narrow-band-mode-decomposition-stnbmd-toolbox) | [[notebook]](https://github.com/wwhenxuan/PySDKit/blob/main/examples/vncmd/stnbmd.ipynb) |
-| [`VTFMTD`](https://github.com/wwhenxuan/PySDKit/blob/main/pysdkit/_tfa/vftmtd.py) (Variational TF Mode Tracking Decomposition) | [[paper]](https://www.sciencedirect.com/science/article/pii/S0165168426001179) | [[code]](https://www.mathworks.com/matlabcentral/fileexchange/183389-variational-time-frequency-mode-tracking-decomposition) | [[notebook]](https://github.com/wwhenxuan/PySDKit/blob/main/examples/tfa/vtfmtd.ipynb) |
+| [`VTFMTD`](https://github.com/wwhenxuan/PySDKit/blob/main/pysdkit/_tfa/vtfmtd.py) (Variational TF Mode Tracking Decomposition) | [[paper]](https://www.sciencedirect.com/science/article/pii/S0165168426001179) | [[code]](https://www.mathworks.com/matlabcentral/fileexchange/183389-variational-time-frequency-mode-tracking-decomposition) | [[notebook]](https://github.com/wwhenxuan/PySDKit/blob/main/examples/tfa/vtfmtd.ipynb) |
+| [`SST`](https://github.com/wwhenxuan/PySDKit/blob/main/pysdkit/_tfa/sst.py) (Synchrosqueezing Transform) | [[paper]](https://doi.org/10.1016/j.sigpro.2014.08.010) | [[code]](https://www.commsp.ee.ic.ac.uk/~mandic/research/sst.htm) | [[notebook]](https://github.com/wwhenxuan/PySDKit/blob/main/examples/tfa/sst.ipynb) |
 | [`SWD`](https://github.com/wwhenxuan/PySDKit/blob/main/pysdkit/_osd/swd.py) (Swarm Decomposition) |   [[paper]](https://doi.org/10.1016/j.sigpro.2016.09.004)    |  [[code]](https://github.com/gkaposto/Swarm-Decomposition)   | [[notebook]](https://github.com/wwhenxuan/PySDKit/blob/main/examples/osd/swd.ipynb) |
 | [`OSD`](https://github.com/wwhenxuan/PySDKit/blob/main/pysdkit/_osd/osd.py) (Optimization-based Signal Decomposition) | [[paper]](https://web.stanford.edu/~boyd/papers/sig_decomp_mprox.html) |   [[code]](https://github.com/cvxgrp/signal-decomposition)   | [[notebook]](https://github.com/wwhenxuan/PySDKit/blob/main/examples/osd/osd_intro.ipynb) |
 | [`STL`](https://github.com/wwhenxuan/PySDKit/blob/main/pysdkit/tsa/_stl.py) (Seasonal-Trend decomposition using LOESS) | [[paper]](https://www.nniiem.ru/file/news/2016/stl-statistical-model.pdf) | [[code]](https://www.statsmodels.org/stable/examples/notebooks/generated/stl_decomposition.html) | [[notebook]](https://github.com/wwhenxuan/PySDKit/blob/main/examples/tsa/stl.ipynb) |