Efel

----------------

- Removed pdf documentation file. Reason: There was no substantial information in the pdf that were not already present in the official doc.
- added an example for using settings, and added this example to the docs
- added the (already implemented) following features to docs:

* check_ais_initiation
* bpap_attenuation
* peak_indices
* AP_rise_indices
* AP_end_indices
* AP_fall_indices
* min_AHP_indices
* AP_begin_indices
* min_between_peaks_indices
* burst_begin_indices
* burst_end_indices
* ADP_peak_indices
* interburst_min_indices
* postburst_min_indices
* postburst_slow_ahp_indices
* postburst_fast_ahp_indices
* postburst_adp_peak_indices
* interburst_15percent_indices
* interburst_20percent_indices
* interburst_25percent_indices
* interburst_30percent_indices
* interburst_40percent_indices
* interburst_60percent_indices
* burst_ISI_indices

---------------

- Reduces redundant dependency tree initializations in cppcore, improving feature extraction performance by up to 2.5x. Ensures getFeatureValues avoids unnecessary resets; use efel.reset to reload dependencies when needed.

---------------

- When stimulus starts at 0 for impedance (which can happen often), use steady_state_voltage_stimend to get holding voltage, and equivalent for holding current.
Since at the end of the stimulus, we expect the current and voltage to vary rapidly around the holding value, this is a good enough proxy to get it.
- implemented test_steady_state_current_stimend, along with documentation and test
- fixed current interpolation
- fixed stim_end value in impedance test data file

----------------

- Adding extracellular features: `"peak_to_valley", "halfwidth", "peak_trough_ratio", "repolarization_slope", "recovery_slope","neg_peak_relative", "pos_peak_relative", "neg_peak_diff", "pos_peak_diff", "neg_image"` and `"pos_image"`
- Add example for extracellular features
- Documentation update to mention features that can be used fo phase analysis: `"AP_phaseslope", "phaseslope_max"`, `"AP_fall_rate", "AP_fall_rate_change", "AP_peak_downstroke", "AP_peak_upstroke", "AP_rise_rate"` and `"AP_rise_rate_change"``

----------------

- Added AP_phaseslope_range to efel.settings as int with default value of 2

----------------

- Fixed edge case (1 spike and no min_AHP_indices dependency) in AP_begin_indices