feat: blob info V2 for tracking pooled blobs

[halfprice]

Description

• Introduce BlobInfoV2, ValidBlobInfoV2 to support storage pool (bucket) blobs alongside regular blobs
• Add PooledBlobChangeStatus and PoolExpired variants to BlobInfoMergeOperand for pool blob lifecycle events
• Wrap existing BlobInfoV1 in versioned BlobInfo enums that route operands to the correct version
• V1 entries auto-upgrade to V2 when a pool operand arrives; regular operands keep V1 as V1
• To track per object blob info for pooled blob, we will create a dedicated table and dedicated per object pooled blob info in follow up PR.

To easy review:

• First commit: simply copy PerObjectBlobInfoV1 to blob_info_v1.rs
• Second commit: copy implementation of BlobInfoV1 & PerObjectBlobInfoV1 to BlobInfoV2 & PerObjectBlobInfoV2 in blob_info_v2.rs.
• Third commit (review focus): updating BlobInfoV2 & PerObjectBlobInfoV2.

Contribute to WAL-1162
Contribute to WAL-1175

Test plan

Unit test

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Release notes

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[halfprice]

Quoting local codex:

can you verify that the third from the last commit is a no-op refactor? Can you also verify that the second from the last commit is simply copy the identical implementation of BlobInfoV1 to BlobInfoV2 and PerObjectBlobInfoV1 to PerObjectBlobInfoV2?

Yes.

For a631793 (refactor: move PerObjectBlobInfoV1 to blob_info_v1.rs), I verified it is a no-op refactor by inspection. The diff only:

• moves PerObjectBlobInfoV1 and its impls from /Users/zhewu/work/walrus_3/crates/walrus-service/src/node/storage/blob_info/mod.rs into /
  Users/zhewu/work/walrus_3/crates/walrus-service/src/node/storage/blob_info/blob_info_v1.rs
• adds the imports needed in the new file
• replaces the old in-module definition with a re-export

I did not find any logic change in that commit.

For 50f7263 (feat: introduce BlobInfoV2 and PerObjectBlobInfoV2 as copies of V1), the answer is also effectively yes, with one small
qualification:

• PerObjectBlobInfoV2 is identical to PerObjectBlobInfoV1 after the V1 -> V2 rename.
• BlobInfoV2 / ValidBlobInfoV2 / PermanentBlobInfoV2 are also identical to the V1 implementation after renaming, except for one comment-
  only change: the copied comment says future changes should go to ValidBlobInfoV3 instead of ValidBlobInfoV2.

The commit also adds the expected module/enum plumbing in crates/walrus-service/src/node/storage/blob_info/
mod.rs so the new V2 types are wired into BlobInfo and PerObjectBlobInfo. Other than that wiring and the comment update, I did not find
behavioral differences.

[halfprice]

@codex review

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Reviewed commit: d50f5176b9

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[mlegner]

Thank you so much for implementing this and structuring it in such a reviewer-friendly way! 🙏

I confirmed that the first two commits are essentially no-ops and then only reviewed the third commit.

Overall, everything looks sensible to me. I have a few detailed suggestions and one larger one concerning the PerObjectBlobInfoV2.

[sadhansood]

Thanks @halfprice, i did a pass but I do not have in depth expertise of this part of the codebase. I'll try to do another one later today.

[halfprice]

Thanks @sadhansood for the

[halfprice]

Hi @mlegner , I think it'll be easier to review the comments commit by commit.

8eba00b: in this commit, I moved PermanentBlobInfo to top module, along with a few other small changes addressing the comment.
ac87a22: in this commit, I moved some of the common function used in both ValidBlobInfoV1 and ValidBlobInfoV2 processing permanent blob to PermanentBlobInfo. Those functions were static function and remained static functions now. They probably be more suitable to be converted to a member method, but I don't want to further complicate this PR.
680d1ab: in this commit, I completely removed PerObjectBlobInfoV2. PerObjectBlobInfo updates in this PR is not really needed: the only place where it can link to BlobInfoV2 is in check_invariant() to check the consistency between BlobInfo and PerObjectBlobInfo. Since creating PerObjectPooledBlobInfo requires creating a new DBMAP, I'll leave all of these to follow up PRs.

In short, what this PR introduces is only the aggregated BlobInfoV2.

[halfprice]

@codex review

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Reviewed commit: 680d1abd18

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[mlegner]

Thanks a lot for the changes, @halfprice. This LGTM. 💯