feat: Fuse partition and metrics filtering into manifest deserialization

[zenfenan]

Closes #3657

Rationale for this change

_open_manifest() currently deserializes all live manifest entries via fetch_manifest_entry() and then applies partitions & metrics filters as a second pass. This materialises the full list before discarding non-matching entries.

This PR adds ManifestFile#prune_manifest_entry() that fuses filtering into the deserialization loop, avoiding the intermediate list allocation for non-matching entries.

Total Entries	Entries Matching Filter	Two-pass Time	Fused Time	Improvement
116k	78 (0.07%)	9.13s	7.18s	-21.3%
438k	1 (~0%)	35.12s	27.81s	-20.8%
823k	4,962 (0.6%)	54.38s	41.38s	-23.9%
18k	269 (1.5%)	1.23s	0.90s	-27.0%
8k	185 (2.2%)	0.57s	0.40s	-30.2%

Are these changes tested?

Yes, existing test suit passes. No behavioral change. Correctness was validated across all benchmark runs (matched entry counts identical between both paths).

Are there any user-facing changes?

No.