feat: DIA-2092: Support reading multiple tasks from each file in a cloud storage

[matt-bernstein]

[x] allow reading multiple tasks from the same file during import storage sync in scan_and_create_links
[x] update get_data for all import storage types to return list[dict] instead of dict
[x] handle blob urls? currently, still assuming only 1 task per file using these. Changing this would have a larger blast radius, would have to read the url at import time to determine how many tasks are in it, and then make up a task format for pointing to an object within a url, and read the url n times for n tasks during normal usage unless it's cached somehow... use blob urls == "Treat every bucket object as a source file", so it doesn't make sense to do this
[x] do the same for LSE S3 and GCS WIF import storage
[x] add test coverage - currently most test coverage for io_storages is in a single tavern file. Each import storage class definitely needs its own coverage for multiple tasks per key, so this'll be pretty lengthy

[sentry]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: label_studio/io_storages/base_models.py

Function	Unhandled Issue
_scan_and_create_links	ValueError: Storage status (in_progress) must be QUEUED to move it IN_PROGRESS io_storages.base... Event Count: 8
_scan_and_create_links	ValueError: Error on key object-detection/processed_videos.json: For GCS your JSON file must be a dictionary with one task. ... Event Count: 3

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[codecov]

Codecov Report

Attention: Patch coverage is 86.74033% with 24 lines in your changes missing coverage. Please review.

Project coverage is 78.53%. Comparing base (665f1b5) to head (9629f22).
Report is 16 commits behind head on develop.

Files with missing lines	Patch %	Lines
label_studio/io_storages/localfiles/models.py	30.00%	7 Missing ⚠️
label_studio/io_storages/redis/models.py	62.50%	6 Missing ⚠️
..._studio/io_storages/tests/test_multitask_import.py	94.00%	3 Missing ⚠️
label_studio/io_storages/azure_blob/models.py	77.77%	2 Missing ⚠️
label_studio/io_storages/base_models.py	80.00%	2 Missing ⚠️
label_studio/io_storages/gcs/models.py	81.81%	2 Missing ⚠️
label_studio/io_storages/s3/models.py	86.66%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7334      +/-   ##
===========================================
+ Coverage    78.40%   78.53%   +0.12%     
===========================================
  Files          193      195       +2     
  Lines        15624    15767     +143     
===========================================
+ Hits         12250    12382     +132     
- Misses        3374     3385      +11     

Flag	Coverage Δ
pytests	78.53% <86.74%> (+0.12%)	⬆️

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[pakelley]

I don't see anything blocking, lgtm

[matt-bernstein]

/fm sync

Workflow run

[matt-bernstein]

/fm sync

Workflow run