feat: unify stac harvester and stac provider functionality

[michaelmattig]

Here is a brief summary of what I did:

[coveralls]

Coverage Report for CI Build 30923912864

Coverage decreased (-0.3%) to 87.262%

Details

• Coverage decreased (-0.3%) from the base build.
• Patch coverage: 935 uncovered changes across 11 files (1827 of 2762 lines covered, 66.15%).
• 8 coverage regressions across 5 files.

Uncovered Changes

Top 10 Files by Coverage Impact	Changed	Covered	%
geoengine/services/src/cli/stac_harvester/harvest.rs	1049	475	45.28%
geoengine/services/src/cli/stac_harvester/discover.rs	739	555	75.1%
geoengine/services/src/datasets/external/stac/common.rs	652	570	87.42%
geoengine/services/src/util/retry.rs	94	32	34.04%
geoengine/services/src/cli/stac_harvester/mod.rs	27	0	0.0%
geoengine/operators/src/source/gdal_worker_process/process_impl.rs	7	6	85.71%
geoengine/services/src/bin/geoengine-cli.rs	1	0	0.0%
geoengine/services/src/cli/stac_import.rs	9	8	88.89%
geoengine/services/src/datasets/external/stac/loading_info.rs	132	131	99.24%
geoengine/services/src/datasets/external/stac/mod.rs	14	13	92.86%
Total (15 files)	2762	1827	66.15%

Coverage Regressions

8 previously-covered lines in 5 files lost coverage.

File	Lines Losing Coverage	Coverage
geoengine/operators/src/cache/shared_cache.rs	2	85.03%
geoengine/operators/src/source/gdal_worker_process/process_impl.rs	2	92.71%
geoengine/services/src/datasets/external/stac/loading_info.rs	2	87.02%
geoengine/services/src/datasets/external/aruna/mock_grpc_server.rs	1	83.12%
geoengine/services/src/datasets/external/stac/mod.rs	1	85.07%

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Coverage Stats

Relevant Lines:	145160
Covered Lines:	126670
Line Coverage:	87.26%
Coverage Strength:	478943.94 hits per line

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💛 - Coveralls