feat(blockstore): expose BloomCacheStatus and add bloom filter Rebuild

[guillaumemichel]

Builds on top of #1183, which stops the Bloom filter cache from activating
after an incomplete AllKeysChan enumeration and adds the (unexported)
capability to report a truncated enumeration.

This PR makes that machinery observable and recoverable from outside the
package:

• Exports the capability as AllKeysChanWithErrer (AllKeysChanWithErr),
  so any Blockstore can report an error that truncated AllKeysChan
  enumeration, and callers can detect it. Forwarded through the same layers as
  in fix(blockstore): don't activate bloom cache if build incomplete #1183 (bloomcache, tqcache, idstore, ValidatingBlockstore); stores that
  don't implement it fall back to today's best-effort behavior.

• Adds BloomCacheStatus (Wait / BloomActive / Rebuild), implemented
  by the value CachedBlockstore returns when a Bloom filter is configured.
  Wait/BloomActive existed but were unreachable on the unexported cache
  type; they're now part of an exported interface, so callers can wait for and
  observe the async initial build.

• Adds Rebuild, to retry after a failed initial build (observable via
  Wait) or refresh a healthy filter. The rebuild runs live: the current
  filter stays active and correct throughout, concurrent writes are mirrored
  into the replacement, and the new filter is swapped in atomically only once a
  complete enumeration proves it authoritative. A failed or cancelled rebuild
  leaves the existing filter in place.

No behavior change for existing callers; all additions are opt-in via the new
interfaces.

[codecov]

Codecov Report

❌ Patch coverage is 90.69767% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.75%. Comparing base (bbf07ab) to head (551d074).

Files with missing lines	Patch %	Lines
blockstore/bloom_cache.go	88.88%	3 Missing and 1 partial ⚠️

@@                      Coverage Diff                       @@
##           fix/bloom-incomplete-build    #1184      +/-   ##
==============================================================
- Coverage                       63.75%   63.75%   -0.01%     
==============================================================
  Files                             269      269              
  Lines                           27027    27047      +20     
==============================================================
+ Hits                            17232    17243      +11     
- Misses                           8081     8086       +5     
- Partials                         1714     1718       +4     

Files with missing lines	Coverage Δ
blockstore/blockstore.go	56.02% <100.00%> (ø)
blockstore/caching.go	100.00% <ø> (ø)
blockstore/idstore.go	68.25% <100.00%> (ø)
blockstore/twoqueue_cache.go	72.46% <100.00%> (ø)
blockstore/validating_blockstore.go	66.66% <100.00%> (ø)
blockstore/bloom_cache.go	73.10% <88.88%> (+3.50%)	⬆️

... and 10 files with indirect coverage changes

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[gammazero]

Everything here looks good.

While not necessary for this PR, it would be if bloomcache.active was changed to a atomic.Bool type.