Sync df55 Iceberg fixes and handle Horizon no-content responses

[osipovartem]

Summary

• Bring the df55 branch up to the commits already pinned by Rustice: file-catalog commit conflict reporting and null-safe transformed/bucket partition pruning.
• Accept successful REST rename responses with either an empty body or Horizon's non-JSON NO_CONTENT payload, while retaining HTTP error details.
• Treat bodyless HEAD 404 as an absent namespace; propagate 403 and other errors. This allows Rustice's lazy Horizon bootstrap to choose the physical namespace without listing all namespaces.

Verification

• REST unit tests for 2xx rename bodies and 4xx responses.
• Loopback HEAD test covers 200, bodyless 404, and 403, with bounded listener waits.
• cargo +1.95.0 clippy -p iceberg-rest-catalog --lib -- -D warnings.
• Rustice live Horizon smoke: Snowflake-created Iceberg v3 table, Rustice rename and INSERT, fresh Rustice read and Snowflake read both returned IDs 1 and 2; disposable table removed and X-Small warehouse suspended.
• Independent read-only review of the full diff approved with no blocking findings.

This PR intentionally includes the earlier df55 commits because they are already used by Rustice but are not yet on embucket-sync-df55.0.0.