perf: RTL Go-native migration — 27 optimizations, DML up to 70-90x

Systematic pass through PRG hot paths, promoting them to Go RTL while
preserving Harbour/FiveSql2 semantics. Full log in
docs/RTL-Go-Native-Migration.md.

Bench (bench_sql) vs 2026-04-08 baseline
 - B1  SELECT *             2,192 → 114   µs   (19x)
 - B6  INNER JOIN           9,291 → 233   µs   (40x)
 - B7  CTE simple           8,037 → 129   µs   (62x)
 - B9  ROW_NUMBER           3,705 → 265   µs   (14x)
 - B10 RANK PARTITION       4,748 → 309   µs   (15x)
 - B12 INSERT (WA cache)    4,319 →  63   µs   (69x)
 - B13 UPDATE (WA cache)    6,144 →  68   µs   (90x)
 - B15 CTE+WIN+JOIN        18,395 → 1,873 µs   (10x)

Infrastructure
 - HbHash O(1) Index preserving insertion order (Harbour KEEPORDER)
 - HbDeepClone Go RTL (scalar-sharing, immutable hash keys)
 - MEMRDD auto-imported via gengo; all Five programs get mem:name driver
 - SQL plan + pcode caches (s_hPlanCache, s_hDmlPcodeCache)
 - Opt-in SqlWACacheEnable — dbUseArea/Close/Commit batched for DML

SQL engine
 - FiveSql2 lexer ported to Go (byte FSM) with combined automatic
   template parameterization (literals → ?, concat queries share plan)
 - Go RTL: SqlDistinct, SqlGroupRows, SqlWindowPartitions,
   SqlWindowSortPartition, SqlWindowAssignRank, SqlComputeAggSimple,
   SqlBulkInsert, SqlBulkUpdate, SqlExprHasAgg, SqlEvalHaving
 - CTE / subquery / driving-table materialize paths use MEMRDD
 - SqlCoerce/SqlCmp/SqlIsTrue helpers moved from PRG to Go
 - SqlBulkUpdate defers Flush when WA cache active (APFS fsync was
   dominant B13 cost — 1.6ms/call → gone)

Correctness fixes uncovered during migration
 - ASort default path now sorts dates/logicals/timestamps (was no-op)
 - ORDER BY default NULL placement matches PRG SqlRowCompare across
   Go fast path; explicit NULLS FIRST/LAST honored by both paths
 - SqlBulkUpdate respects EXCLUSIVE vs SHARED mode record locks
 - SqlCmp/SqlCmpEq normalize NumInt vs Double (caught by test 6b)

Verification
 - go test ./...              ALL PASS
 - FiveSql2 test_sql1999      43/43
 - tests/compat_harbour       56/56 (+5 new: ASort dates/logicals,
                              AScan int cross-type)
 - Regression test test_null_order.prg for ORDER BY NULL ordering

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/compat_harbour.prg

@@ -330,11 +330,31 @@ STATIC PROCEDURE TestArrayHash()
    ASort(a,,, {|x,y| x > y})
    Assert("9d ASort desc: {3,2,1}", a[1] == 3 .AND. a[2] == 2 .AND. a[3] == 1)
 
+   // ASort dates (default, no block — formerly no-op, now sorts julian)
+   a := { CToD("2026-03-15"), CToD("2024-01-10"), CToD("2025-07-01") }
+   ASort(a)
+   Assert("9c1 ASort dates ascending", ;
+      a[1] == CToD("2024-01-10") .AND. ;
+      a[2] == CToD("2025-07-01") .AND. ;
+      a[3] == CToD("2026-03-15"))
+
+   // ASort logicals (default — .F. < .T.)
+   a := { .T., .F., .T., .F. }
+   ASort(a)
+   Assert("9c2 ASort logicals: F,F,T,T", ;
+      !a[1] .AND. !a[2] .AND. a[3] .AND. a[4])
+
    // AScan
    a := {"alice", "bob", "charlie"}
    Assert("9e AScan: found 'bob' at 2", AScan(a, "bob") == 2)
    Assert("9f AScan: 'dave' not found", AScan(a, "dave") == 0)
 
+   // AScan numeric fast-path
+   a := { 10, 20, 30, 40 }
+   Assert("9e1 AScan int found", AScan(a, 30) == 3)
+   Assert("9e2 AScan int cross-type (double lookup)", AScan(a, 30.0) == 3)
+   Assert("9e3 AScan int not found", AScan(a, 99) == 0)
+
    // AEval with mutable closure capture (Harbour: closures share outer locals)
    nSum := 0
    AEval({10, 20, 30}, {|x| nSum += x})