fix retain, replace by filter

[lightsing]

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[Copilot]

Pull request overview

This PR replaces the previous in-place “retain/purge” approach with a “filter-to-new” approach for removing pending attestations, updating the core timestamp API plus SDK/CLI purge flows accordingly.

Changes:

• Core: replace retain_attestations*-style logic with a new filter_attestations that returns a modified copy, and update purge_pending to return a filtered Timestamp.
• SDK: rework pending purge into filter_pending* APIs that return a new DetachedTimestamp plus a list of purged URIs.
• CLI: update the purge command to use the new SDK filtering API and write a new proof to disk.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
packages/sdk-rs/src/purge.rs	Introduces filter_pending* returning a new timestamp + purged URI list.
crates/core/src/codec/v1/timestamp.rs	Adds filter_attestations (copy-based filtering) and updates pending-related iteration/APIs.
crates/core/src/codec/v1/digest.rs	Makes DigestHeader Copy.
crates/cli/src/commands/purge.rs	Switches CLI purge implementation to the new filter-based approach.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

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