VarBin: build views straight into a VarBinViewBuilder - #9127

Appending a `VarBin` array to a `VarBinViewBuilder` canonicalized it first, which
built the views, wrapped them in a `VarBinViewArray` the builder immediately
unwrapped, and then had `append_varbinview_array` rewrite every view to rebase
its buffer index onto the builder's.

Number the buffer up front instead: `varbin_decode_views` takes the index the
pushed buffer will land at, so the views come out already correct and the append
is one view per row plus a buffer push. `varbin_to_canonical` now shares that
helper, which also shrinks what `match_each_integer_ptype!` duplicates.

A builder configured to compact still goes the canonical route — it chooses per
buffer whether to keep, slice or rewrite it by measuring the finished views, and
`push_buffer_and_adjusted_views` would bypass that.

chunk_array_builder, fastest of 100 samples, 3 runs each:

| benchmark (rows x chunks)             | before  | after   | speedup |
| ------------------------------------- | ------- | ------- | ------- |
| varbin_to_varbinview_builder 10x1000  | 313 µs  | 204 µs  | 1.53x   |
| varbin_to_varbinview_builder 100x100  | 87.3 µs | 69.5 µs | 1.26x   |
| varbin_to_varbinview_builder 1000x10  | 58.6 µs | 54.8 µs | 1.07x   |
| varbin_opt_to_varbinview_bldr 10x1000 | 378 µs  | 266 µs  | 1.42x   |
| varbin_into_canonical 10x1000         | 357 µs  | 253 µs  | 1.41x   |

The last row is the control: it never touches the builder, so its gain is from
the shared-helper extraction alone. Relative to it, the append itself drops from
0.88x to 0.81x of a canonicalization.

Signed-off-by: Robert Kruszewski <github@robertk.io>

Signed-off-by: Robert Kruszewski <github@robertk.io>

Signed-off-by: Robert Kruszewski <github@robertk.io>