[performance] Trim stop_times before stop time interpolation

[yiyange]

Stop time interpolation works on the entire stop_times df, majority of which will be tossed later based on given requested time range.

Trimming down stop_times before passing it to the stop time interpolation step increases performance by a huge amount.

Here are some evidence of the performance gain on the pt.paths.generate_summary_graph_elements step:

gtfs id	current version	with trimming
f-9q9-bart	9.0s, 97 edges, 50 stops	3.8s, 97 edges, 50 stops
f-9q9-actransit	132.0s, 5670 edges, 5050 stops	59.8s, 5670 edges, 5050 stops
f-9q8y-sfmta	131.3s, 3806 edges, 3409 stops	66.7s, 3806 edges, 3409 stops
f-9qb-goldengatetransit	10.6s, 519 edges, 473 stops	7.5s, 519 edges, 473 stops
f-9qc-fairfield~ca~us	5.0s, 280 edges, 245 stops	3.1s, 280 edges, 245 stops
f-9qc0-soltrans~ca~us	6.6s, 475 edges, 408 stops	4.3s, 475 edges, 408 stops
f-9qc-westcat~ca~us	6.2s, 263 edges, 220 stops	3.6s, 263 edges, 220 stops
f-9-amtrak***	14.5s, 306 edges, 260 stops	12.0s, 306 edges, 260 stops

[yiyange]

I ran similar process using UrbanAccess. Here is part of the comparison if you are interested

gtfs id	UrbanAccess	PT with trimming
f-9q9-bart	4.0s, 97 edges, 50 stops	3.8s, 97 edges, 50 stops
f-9q9-actransit	Failed	59.8s, 5670 edges, 5050 stops
f-9q8y-sfmta	97.4s, 3806 edges, 3409 stops	66.7s, 3806 edges, 3409 stops
f-9qb-goldengatetransit	Failed	7.5s, 519 edges, 473 stops
f-9qc-fairfield~ca~us	4.1s, 297 unique edges, 250 stops	3.1s, 280 edges, 245 stops
f-9qc0-soltrans~ca~us	3.2s, 473 unique edges, 407 stops	4.3s, 475 edges, 408 stops
f-9qc-westcat~ca~us	2.6s, 263 edges, 220 stops	3.6s, 263 edges, 220 stops
f-9-amtrak***	Failed	12.0s, 306 edges, 260 stops

[codecov[bot]]

Codecov Report

Merging #93 into master will decrease coverage by 0.28%. The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master      #93      +/-   ##
==========================================
- Coverage   91.91%   91.62%   -0.29%     
==========================================
  Files          12       12              
  Lines         866      872       +6     
==========================================
+ Hits          796      799       +3     
- Misses         70       73       +3

Impacted Files	Coverage Δ
peartree/summarizer.py	91.44% <85.71%> (+0.35%)	:arrow_up:
peartree/parallel.py	96.4% <0%> (-2.16%)	:arrow_down:

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[kuanb]

Again, thank you so much! Amazing.

[yiyange]

Hmm, I wonder why codecov dropped...