Add byte-budget construction for Bloom filters

[yuweih205]

Fixes #829.

Adds cuco::bloom_filter_bytes construction for dynamic-extent Bloom filters. The value is an upper-bound storage budget: allocation is rounded down to whole filter blocks and capped at max_size(), so it never exceeds the requested bytes. Budgets smaller than one block fail before allocation.

The existing block-count constructor remains unchanged. Coverage is folded into the existing Bloom filter policy test rather than a separate test target.

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[sleeepyjack]

Hi @yuweih205,

Thanks for contributing to cuco!
@PointKernel and I discussed the topic offline and settled on a simpler approach:
Instead of allowing the user to go both ways aka provide a lower-bound or upper-bound size in bytes, we only really need the upper-bound case which can be handled through the new ctor overload.

In short, 'bloom_filter(bloom_filter_bytes size)' allocates a filter that is always smaller or equal to 'size'; never exceeding it.
This means we can also remove the 'aligned_size' helper and the extent factory, making the API much simpler.

One small nit: I would suggest to rename the strong type for the filter size to `bloom_filter_bytes' as it is a bit shorter.

Do you agree with these changes? Happy to discuss and thanks again for your work on this!

[yuweih205]

Agreed—updated. bloom_filter_bytes is now an upper-bound budget: the constructor rounds down to whole blocks, caps at max_size(), and is available only for dynamic extents. I removed aligned_size, the extent factory, and the standalone sizing test, folding the minimal coverage into the existing policy test.

[sleeepyjack]

/ok to test c80884c