[DOC] update for download page 2512 release [skip ci]

[nvliyuan]

update the download doc for 2512 release
Signed-off-by: liyuan yuali@nvidia.com

[nvliyuan]

For more details info:

• Iceberg enhancements including DML operations (delete, update, merge) for merge-on-read tables, partition transforms (year/month/day/hour/truncate), and write operations enabled by default (#13725, #13755, #13726, #13797, #13891)
• Delta Lake clustered tables DML support including update, merge, and delete operations with deletion vector enabled GPU by default [Databricks] (#13822, #13814, #13859, #13843)
• Join improvements including support for left-outer joins with no columns, new join strategies with logging and heuristic configurations, and improved gather map ordering (#13921, #13717, #13929)
• CSV support for GBK encoded data (#13754)
• Refine GpuTaskMetrics over the spill framework #13905
• Fix race condition due to premature disk handle exposure #13919

[greptile-apps]

Greptile Overview

Greptile Summary

Documentation update for the RAPIDS Accelerator for Apache Spark v25.12.0 release.

• Updated docs/download.md from v25.10.0 to v25.12.0 with new download links, Maven coordinates, and release notes highlighting Iceberg DML operations, Delta Lake clustered tables DML support, join improvements, and bug fixes
• Archived the v25.10.0 release documentation in docs/archive.md
• Added Apache Spark 3.5.7 to the list of supported Spark versions in v25.12.0

Confidence Score: 5/5

• This PR is a documentation-only change with no code impact and is safe to merge.
• This is a straightforward documentation update for a new release. All version numbers, URLs, and Maven coordinates are consistent. The changes follow the established pattern from previous releases.
• No files require special attention.

Important Files Changed

File Analysis

Filename	Score	Overview
docs/download.md	5/5	Updated download page from v25.10.0 to v25.12.0 with new release notes, download links, signature verification commands, and added Spark 3.5.7 to supported versions.
docs/archive.md	5/5	Archived the v25.10.0 release documentation at the top of the archive page with its complete release notes, download links, and requirements.

Sequence Diagram

sequenceDiagram
    participant User
    participant Download as docs/download.md
    participant Archive as docs/archive.md
    
    Note over Download: v25.10.0 → v25.12.0
    Download->>Archive: v25.10.0 release info moved
    Note over Download: Updated download links
    Note over Download: Updated Maven coordinates
    Note over Download: New release notes for v25.12.0
    Note over Archive: v25.10.0 preserved at top

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[greptile-apps]

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[NvTimLiu]

LGTM

The base branch was changed.

[NvTimLiu]

Oops, this change must target to the branch "release/25.12" @nvliyuan

The base branch was changed.

[greptile-apps]

Skipped: This PR changes more files than the configured file change limit: (133 files found, 100 file limit)