fix(spark): resolve vortex.workerThreads case-insensitively

[jackylee-ch]

A read option set as vortex.workerThreads never reached the native runtime.

VortexTable.newScanBuilder merges the CaseInsensitiveStringMap Spark hands it into the format options. That map lower-cases its keys in the constructor and entrySet() returns the lower-cased delegate, so the option arrives spelled vortex.workerthreads — while VortexScanBuilder seeds the camelCase spelling with the default of 4. Both keys end up in the map and the case-sensitive getOrDefault always read the default one, silently ignoring the user's value.

Also validates the value. It was a bare Integer.parseInt, so a non-numeric value failed inside the executor task with NumberFormatException: For input string: "eight" — naming neither the option nor the accepted range — and a negative value only failed later in the native runtime.

Tests

New VortexPartitionReaderFactoryTest (JVM-only, no session): default, camelCase key, lower-cased key, zero, whitespace, non-numeric and negative.

• ./gradlew :vortex-spark_2.13:test --tests 'dev.vortex.spark.read.VortexPartitionReaderFactoryTest' — 7/7 pass
• ./gradlew :vortex-spark_2.12:test ... — 7/7 pass
• VortexSqlTest and VortexFilterPushdownTest (both Scala versions) — pass, unchanged
• spotlessCheck (both) and javadoc — clean

[robert3005]

I thought we can make this a CaseInsensitiveStringMap, and probably go higher in the call stack and start with CaseInsensitiveStringMap wherever those options originate from

[jackylee-ch]

CaseInsensitiveStringMap isn't Serializable, and formatOptions crosses two serialization boundaries — the VortexPartitionReaderFactory field and the VortexFilePartition record component.

How about a small VortexOptions wrapper, along the lines of Spark's own ParquetOptions? FileSourceOptions is Serializable, holds its CaseInsensitiveMap as transient, and resolves the options it needs into plain fields up front — that gets us case-insensitive lookup and serializability at the same time, and gives the options a single home instead of string literals at each call site.

Happy to do it here, or as a follow-up if you'd rather keep this PR to the one-line fix.

[jackylee-ch]

Opened #9191 with a VortexOptions type along these lines — case-insensitive lookup for every option, Serializable with a transient view like ParquetOptions, threaded through the read and write paths. Leaving this PR as the minimal fix; happy to close it in favour of #9191 if you prefer.