Michał Chojnowski 88c9af3c80 sstables/trie: perform the BTI-encoding of position_in_partition eagerly ...

Applying lazy evaluation to the BTI encoding of clustering keys
was probably a bad default.
The benefits are dubious (because it's quite likely that the laziness
won't allow us to avoid that much work), but the overhead needed to
implement the laziness is large and immediate.

In this patch we get rid of the laziness.
We rewrite lazy_comparable_bytes_from_clustering_position
so that it performs the translation eagerly,
all components to a single bytes_ostream.

Note: the name *lazy*_comparable_bytes_from_clustering_position
stays, because the interface is still lazy.

perf_bti_key_translation:

Before:
test                            iterations      median         mad         min         max      allocs       tasks        inst      cycles
lcb_mismatch_test.lcb_mismatch        9233   109.930us     0.000ns   109.930us   109.930us    4356.000       0.000   2615394.3    614709.6

After:
test                            iterations      median         mad         min         max      allocs       tasks        inst      cycles
lcb_mismatch_test.lcb_mismatch       50952    19.487us     0.000ns    19.487us    19.487us     198.000       0.000    603120.1    109042.9

2025-09-29 04:10:40 +02:00

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