Improve speed of convertSequences() and get1BlockSummary() using RVV

[zijianli1234]

This PR improves the speed of convertSequences() and get1BlockSummary() when compiled with RVV support on RISCV and pass test on qemu with vlen=128,256,512. Modeled after PR #4232 , this change brings similar functionality to the RISC-V architecture.

For illustration, here are some benchmark numbers, on a Spacemit(R) X60 @1.6 Ghz, using enwik5 (100KB) and the sequences produced by level 5.

dataset	compiler	convertSequences (1st block) on dev	convertSequences (1st block) with RVV enabled	get1BlockSummary (1st block) on dev	get1BlockSummary (1st block) with RVV enabled
enwik5, level 5	gcc v14.2	1328.0 MB/s	2149.9 MB/s	1715.6 MB/s	2783.6 MB/s

This vector code can reduce the overhead of translating the Sequence public format into the internal one to optimize perference on RISCV.

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[Cyan4973]

It looks great @zijianli1234 !
It's clean and sufficiently documented.

Please note that the CLA signing process is compulsory to merge your contribution,
we'll have to wait for this step to complete in order to move forward.

[zijianli1234]

Hi, @Cyan4973 ,I have signed CLA, please move forward,thank you so much.