Add LoadFromDatabase convenience methods (#4182)

[rAJt-11]

Adds LoadFromDatabase extension methods on DataOperationsCatalog, mirroring the existing LoadFromTextFile convenience API. This collapses the current three-step database-loading pattern into a single call.

Before:
var loader = mlContext.Data.CreateDatabaseLoader();
var source = new DatabaseSource(SqlClientFactory.Instance, connString, "SELECT * FROM Iris");
var data = loader.Load(source);

After:
var data = mlContext.Data.LoadFromDatabase(SqlClientFactory.Instance, connString, "SELECT * FROM Iris");
LoadFromDatabase(DatabaseSource source)
LoadFromDatabase(DbProviderFactory providerFactory, string connectionString, string commandText)
LoadFromDatabase(DbProviderFactory providerFactory, string connectionString, string commandText, int commandTimeoutInSeconds)

Why this approach
I followed the established LoadFromTextFile pattern in TextLoaderSaverCatalog so the new API stays consistent with the rest of the catalog. The methods simply compose the existing CreateDatabaseLoader() and Load(DatabaseSource) no new loading logic and argument validation is delegated to the existing DatabaseSource constructor.

Tests
Added IrisVectorLightGbmUsingLoadFromDatabase to DatabaseLoaderTests.cs, exercising the new API end-to-end through a LightGBM training pipeline.

[rAJt-11]

@dotnet-policy-service agree

[rAJt-11]

The failing DatabaseLoaderTests.Iris* tests (IrisLightGbm, IrisVectorLightGbm, IrisLightGbmWithTimeout, IrisSdcaMaximumEntropy) are failing due to the known LocalDB iris.mdf read-only attach issue tracked in #7657 — they fail independently of this change (my new LoadFromDatabaseLoadsExpectedData test uses in-memory SQLite and is unaffected). Could a maintainer confirm and/or re-run once #7657 is sorted?

[codecov]

Codecov Report

❌ Patch coverage is 97.29730% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.90%. Comparing base (13dc9c5) to head (95d4583).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ata/DataLoadSave/Database/DatabaseLoaderCatalog.cs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7666   +/-   ##
=======================================
  Coverage   69.89%   69.90%           
=======================================
  Files        1487     1487           
  Lines      276323   276360   +37     
  Branches    28295    28296    +1     
=======================================
+ Hits       193142   193183   +41     
+ Misses      75694    75689    -5     
- Partials     7487     7488    +1     

Flag	Coverage Δ
Debug	69.90% <97.29%> (+<0.01%)	⬆️
production	64.08% <66.66%> (+<0.01%)	⬆️
test	89.84% <100.00%> (+<0.01%)	⬆️

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

Files with missing lines	Coverage Δ
test/Microsoft.ML.Tests/DatabaseLoaderTests.cs	91.98% <100.00%> (+1.07%)	⬆️
...ata/DataLoadSave/Database/DatabaseLoaderCatalog.cs	91.66% <66.66%> (-8.34%)	⬇️

... and 7 files with indirect coverage changes

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