fix: persist iceberg namespace metadata updates

[ferhatelmas]

What kind of change does this PR introduce?

Bug fix

What is the current behavior?

Iceberg create namespace behaves partially idempotent but ignores metadata.

What is the new behavior?

Merge metadata correctly and return stored metadata back to the client.

[Copilot]

Pull request overview

Fixes Iceberg namespace creation idempotency by ensuring namespace metadata/properties are persisted/merged on repeated creates, and by returning the stored (merged) metadata back to the client.

Changes:

• Merge iceberg_namespaces.metadata on createNamespace conflict upsert and return the stored row.
• Return persisted namespace metadata in TenantAwareRestCatalog.createNamespace responses.
• Add an integration test covering metadata merge behavior when creating an existing namespace.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/test/iceberg.test.ts	Adds a test validating metadata merge + load behavior for existing namespaces (also adjusts imports).
src/storage/protocols/iceberg/knex.ts	Updates namespace upsert to merge metadata and return the stored row.
src/storage/protocols/iceberg/catalog/tenant-catalog.ts	Returns stored namespace metadata instead of echoing request properties.

Comments suppressed due to low confidence (1)

src/test/iceberg.test.ts:3

• ErrorCode is imported but never used in this test file. This will fail Biome/TS linting (noUnusedImports); remove ErrorCode from the import or add an assertion that actually uses it.

import assert from 'node:assert'
import { PutObjectCommand, S3Client } from '@aws-sdk/client-s3'
import { isS3Error } from '@internal/errors'

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[coveralls]

Coverage Report for CI Build 25672873628

Coverage increased (+0.04%) to 74.296%

Details

• Coverage increased (+0.04%) from the base build.
• Patch coverage: 2 of 2 lines across 2 files are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	10284
Covered Lines:	8047
Line Coverage:	78.25%
Relevant Branches:	5943
Covered Branches:	4009
Branch Coverage:	67.46%
Branches in Coverage %:	Yes
Coverage Strength:	411.07 hits per line

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