core: stdcm fixes

[eckter]

• We need more accuracy when finding accelerating stops (EDIT: reverted because it's not that easy: Discontinuity in mareco space caused by accelerating slope differences #3140)
• Fix a "typo" / small mistake, the wrong distance value was used to evaluate standard allowance time

[codecov]

Codecov Report

Merging #3139 (eadff7e) into dev (724ab82) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##                dev    #3139   +/-   ##
=========================================
  Coverage     38.52%   38.52%           
  Complexity     1709     1709           
=========================================
  Files           620      620           
  Lines         19663    19663           
  Branches       2589     2589           
=========================================
  Hits           7575     7575           
  Misses        11682    11682           
  Partials        406      406           

Flag	Coverage Δ
core	83.92% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...in/java/fr/sncf/osrd/stdcm/graph/DelayManager.java	100.00% <100.00%> (ø)
...ava/fr/sncf/osrd/stdcm/graph/STDCMEdgeBuilder.java	98.68% <100.00%> (ø)
...main/java/fr/sncf/osrd/stdcm/graph/STDCMGraph.java	96.55% <100.00%> (ø)

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