Add batch decode for RLE (FLOAT/DOUBLE) and GORILLA_V1 encodings #1071

PR #1068 introduced C++ FLOAT/DOUBLE RLE (FloatRLEDecoder / DoubleRLEDecoder in cpp/src/encoding/float_rle_decoder.h) and GORILLA_V1 (FloatGorillaV1Decoder / DoubleGorillaV1Decoder in cpp/src/encoding/gorilla_v1_decoder.h). Both decode one value at a time and never override the read_batch_* methods, so Decoder::read_batch_double / read_batch_int64 / ... (cpp/src/encoding/decoder.h) fall back to a per-value loop over read_double / read_int64.

Existing codecs already received batch decode: PLAIN in #823, GORILLA and TS_2DIFF in #898. The newly added encodings were missed.

Impact

Profiling a wide-table read (5214 columns, RLE-encoded) shows decode dominating the read path: DoubleRLEDecoder::read_double ~43% and Int64RleDecoder::read_int64 (time column) ~38%, essentially all inside the per-value loop.

Proposed changes

1. Int64RleDecoder / Int32RleDecoder (cpp/src/encoding/int64_rle_decoder.h / int32_rle_decoder.h): add read_batch_int64 / read_batch_int32. read_int has two natural batch cases:

   • RLE run (is_rle_run_): the next current_count_ values are all the same rle_value_, so fill the output range in one pass.
   • bit-packing: current_buffer_ already holds the fully unpacked group; memcpy the remaining current_count_ values.
     This benefits both the time column (which uses Int64RleDecoder directly) and the FLOAT/DOUBLE value columns (which wrap it).

2. FloatRLEDecoder / DoubleRLEDecoder: add read_batch_float / read_batch_double overrides that batch-decode the inner int values and then apply the per-value value_at scaling (which depends on page_pos_, so the scaling itself stays per-value).

3. GorillaV1DecoderBase: add read_batch_* overrides following the pattern already in GorillaDecoder (cpp/src/encoding/gorilla_decoder.h).