Add stopsWithRegularTransfers build config parameter

[t2gran]

Note: This PR builds on top of #7425 and should be merged after that PR.

Note: I do not intend to merge this, unless this feature is requested from someone else, we
will merge this into Enturs CI/DI pipeline. We need this until there is a better fix for this. We intend
to work on that soon.

Summary

Introduces a new (experimental) build configuration parameter stopsWithRegularTransfers that
allows operators to explicitly list stop IDs for which regular transfers are always pre-computed
during graph build, even if those stops have no scheduled trips in the static data.

This is a targeted workaround for stops that are unused in static GTFS/NeTEx data but may be
visited at runtime via real-time updates (e.g. a platform a train can be re-routed to). Without
this, such stops are excluded from transfer pre-computation and become unreachable islands when a
real-time update routes a trip to them. The parameter is marked experimental and is intended
as a temporary measure until automatic transfer updates driven by real-time data are implemented.

Configuration

build-config.json

{
  "stopsWithRegularTransfers": ["RB:NSR:Quay:102541", "RB:NSR:Quay:209876"]
}

Documentation

• doc/user/BuildConfiguration.md updated with the new parameter entry, description, and
  experimental warning.

Breaking Changes

None. The new parameter is optional with an empty-list default; existing behaviour is unchanged.

Testing

Unit Tests

• Additional unit tests for the new stopsWithRegularTransfers path not yet added — marked experimental.
• The PatternNearbyStopFilter logic change (removing the feature-flag guard on
  isSometimesUsedRealtime) is covered by the existing filter tests.

Manual Testing

The feature has been tested manually and works.

Documentation

• ✅ Code follows OTP style guidelines (Prettier, JavaDoc)
• ✅ Java Documentation updated for new public fields and methods
• ✅ Configuration option documented in BuildConfiguration.md

Changelog

• ✅ Relevant to operators using real-time trip re-routing to platforms not in static data.
  Should be included in the changelog as an experimental build-config addition.

Bumping the serialization version id

• ✅ The build configuration is changed, so bumping the serialization version is required.

Note The +Bump Serialization Id label should be set if this is merged, but due to some limitation in our CI/DI pipeline I will wait with this until we have decided to merge this - hopefully we are not merging this.

[codecov]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.33%. Comparing base (a8bc029) to head (5d40a8d).
⚠️ Report is 6 commits behind head on dev-2.x.

Files with missing lines	Patch %	Lines
...odule/transfer/filter/PatternNearbyStopFilter.java	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             dev-2.x    #7426   +/-   ##
==========================================
  Coverage      71.32%   71.33%           
  Complexity     21018    21018           
==========================================
  Files           2339     2339           
  Lines          86908    86928   +20     
  Branches        8605     8606    +1     
==========================================
+ Hits           61991    62007   +16     
- Misses         21919    21920    +1     
- Partials        2998     3001    +3     

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