feat(flashback): add flashback service

[runkelcorey]

Asana Task

What changes does this PR propose?

Defines a new docker service flashback.

How were these changes validated?

1. Unit tests for data issues and networking issues for each module
2. Ran docker service without issues

What questions should reviewers consider?

1. Is the CDN url the best place to get our VehiclePositions feed? Can I get it directly from concentrate or RTR (before it enters the API)?
2. What edge cases are missing from testing?
3. Are there significant efficiencies to be gained in the async event loop?
4. Are there better alternatives to the in-memory polars dataframe that I've used to manage state?

[github-actions]

LCOV of commit 356aebb during Continuous Integration (Python) #1734

Summary coverage rate:
  lines......: 62.4% (3407 of 5463 lines)
  functions..: 28.6% (261 of 912 functions)
  branches...: no data found

Files changed coverage rate:
                                                                                     |Lines       |Functions  |Branches    
  Filename                                                                           |Rate     Num|Rate    Num|Rate     Num
  =========================================================================================================================
  src/lamp_py/flashback/events.py                                                    | 100%     51|50.0%     6|    -      0
  src/lamp_py/flashback/io.py                                                        | 100%     44|50.0%     6|    -      0
  src/lamp_py/ingestion/convert_gtfs_rt.py                                           |45.8%    236|19.2%    26|    -      0
  src/lamp_py/runtime_utils/remote_files.py                                          | 100%     73|50.0%     6|    -      0

[github-actions]

LCOV of commit 7d347f0 during Continuous Integration (Python) #1735

Summary coverage rate:
  lines......: 62.2% (3399 of 5463 lines)
  functions..: 28.6% (261 of 912 functions)
  branches...: no data found

Files changed coverage rate:
                                                                                     |Lines       |Functions  |Branches    
  Filename                                                                           |Rate     Num|Rate    Num|Rate     Num
  =========================================================================================================================
  src/lamp_py/flashback/events.py                                                    | 100%     51|50.0%     6|    -      0
  src/lamp_py/flashback/io.py                                                        | 100%     44|50.0%     6|    -      0
  src/lamp_py/ingestion/convert_gtfs_rt.py                                           |45.8%    236|19.2%    26|    -      0
  src/lamp_py/runtime_utils/remote_files.py                                          | 100%     73|50.0%     6|    -      0