fix(stream): preserve zero reorg settings from API

[dumanoglu1]

Summary

• Preserve API-returned 0 values for fix_block_reorgs and keep_distance_from_tip instead of converting them to null
• Move the reorg-setting hydration into a small helper so the zero-value behavior has direct unit coverage
• Add a regression test for both stream reorg fields when the API returns 0

Fixes #84.

Testing

• git diff --check
• go test ./internal/provider -run TestUpdateStreamReorgSettingsFromAPIPreservesZeroValues -count=1 was attempted locally, but Go is not installed in this Windows environment (go command not found).