Use 1024-value pco pages in btrblocks float/integer schemes

The btrblocks PcoScheme for floats and integers compressed with an 8192-
value page size. Shrinking the page to 1024 keeps the per-row size
essentially unchanged (~0.03 bits/value for f64, ~0.07 bits/value for
i64 in the new pcodec_page_size bench) while shrinking the decode window
8x for random access via scalar_at.

Signed-off-by: Claude <noreply@anthropic.com>

Author: claude

vortex-btrblocks/src/schemes/float.rs

@@ -319,7 +319,7 @@ impl Scheme for PcoScheme {
         Ok(vortex_pco::Pco::from_primitive(
             data.array_as_primitive(),
             pco::DEFAULT_COMPRESSION_LEVEL,
-            8192,
+            1024,
             exec_ctx,
         )?
         .into_array())

vortex-btrblocks/src/schemes/integer.rs

@@ -813,7 +813,7 @@ impl Scheme for PcoScheme {
         Ok(vortex_pco::Pco::from_primitive(
             data.array_as_primitive(),
             pco::DEFAULT_COMPRESSION_LEVEL,
-            8192,
+            1024,
             exec_ctx,
         )?
         .into_array())