build: upgrade to Lance 12.0.0-beta.18 and lance-namespace 0.11.1

[FANNG1]

Summary

Upgrades lance-core from 11.0.0-beta.21 to 12.0.0-beta.18. lance-core 12.x is built against lance-namespace 0.11.1, so lance-namespace moves from 0.8.6 to 0.11.1 in the same change — keeping 0.8.6 fails to compile the tests, because DirectoryNamespace (shipped inside lance-core) references response types that do not exist in 0.8.6.

This is a dependency upgrade only; no new connector features.

Behavior changes absorbed

Lance/namespace change	What this PR does
LanceNamespace.queryTable returns QueryTableResponse instead of byte[]; namespaceExists/tableExists return responses	Unwrap with .getData(); update the two test fakes
Update.updateMode is now mandatory — the transaction protobuf cannot persist "absent" distinctly from RewriteRows, so the JNI rejects an empty mode	Position-delta writes (SparkPositionDeltaWrite, 3.4 and 3.5) state RewriteRows explicitly, which is what an absent mode always meant
Lance's default file format version is now 2.2, which rejects legacy (v1) blob columns outright	A table that requests <col>.lance.encoding = 'blob' without pinning file_format_version is now created at 2.1, so it keeps the documented v1 behavior instead of failing the write
stable / next resolve to 2.2 or newer	BlobUtils.fileFormatSupportsBlobV2 recognizes them, so those tables get blob v2 instead of falling through to v1 and being rejected at write time
Lance rejects null struct values at file format version 2.0 instead of silently reading them back as non-null structs with null children	testNullStructV2_0ReadsAsEmptyStruct becomes testNullStructV2_0IsRejected
STABLE resolves to 2.2	The two STABLE assertions in BaseSparkConnectorWriteTest no longer hard-code 2.0/2.1

The blob-encoding rule is the only user-visible change, and it was chosen to keep existing pipelines byte-identical: without it, every CREATE TABLE ... TBLPROPERTIES ('x.lance.encoding' = 'blob') that does not pin a version would start failing. Users who want blob v2 already have to set file_format_version explicitly, per the docs. docs/src/config.md and docs/src/operations/ddl/create-table.md are updated.

Testing

Full module test suites, all green:

• lance-spark-3.5_2.12 — 1400 tests, 0 failures, 0 errors
• lance-spark-3.4_2.12 — 1253 tests, 0 failures, 0 errors
• lance-spark-4.2_2.13 — 1456 tests, 0 failures, 0 errors
• whole reactor test-compile passes; spotless:check clean

https://claude.ai/code/session_011gFXXNur56ZyJhu3qdRMcr

[lance-gatekeeper]

✅ Gate recommendation: approve.

The dependency and API adaptations match Lance 12: namespace responses are unwrapped, position deltas state RewriteRows, and unversioned legacy blob requests pin to 2.1 while stable/next select blob v2. Keeping those unversioned tables on 2.1 is preferable to silently migrating them to blob v2 because it preserves the existing table contract while explicit table or catalog versions remain authoritative. The changed paths are documented and covered by real-dataset tests across representative Spark/Scala seams.