Integrate fast MLX kernel for SDPA with long seqlen

[EricLBuehler]

Benchmarks to come in #903!

[github-actions]

Code Metrics Report

  ===============================================================================
 Language            Files        Lines         Code     Comments       Blanks
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 C Header                2           35           28            0            7
 Dockerfile              1           41           22           10            9
 Happy                   1          442          369            0           73
 JSON                   12          105          104            0            1
 Python                 53         2274         1949           63          262
 Shell                   1           57           22           18           17
 TOML                   18          583          520            2           61
 YAML                    2           21           19            2            0
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 Jupyter Notebooks       4            0            0            0            0
 |- Markdown             2           77           32           31           14
 |- Python               2          196          169            1           26
 (Total)                            273          201           32           40
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 Markdown               40         3009            0         2286          723
 |- BASH                 6          101           98            0            3
 |- JSON                 1           12           12            0            0
 |- Python               6          114          102            0           12
 |- Rust                10          361          306            0           55
 |- TOML                 2           75           63            0           12
 (Total)                           3672          581         2286          805
-------------------------------------------------------------------------------
 Rust                  280        85018        76288         1765         6965
 |- Markdown           136         1436           25         1307          104
 (Total)                          86454        76313         3072         7069
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 Total                 415        91585        79321         4146         8118
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