docs: fix TiKV RocksDB block-size defaults

[doc-claw-bot]

What is changed, added or deleted? (Required)

Fixes the outdated default RocksDB block-size value in the following TiKV docs:

• storage-engine/rocksdb-overview.md
• tune-tikv-memory-performance.md

These documents said the default block size is 64 KB / 64KB, but the TiKV config template uses 32KB for rocksdb.defaultcf and rocksdb.writecf.

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• master (the latest development version)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):
  • https://docs.pingcap.com/tidb/stable/tikv-configuration-file/#block-size
  • https://raw.githubusercontent.com/tikv/tikv/master/etc/config-template.toml
  • https://raw.githubusercontent.com/tikv/tikv/release-8.5/etc/config-template.toml

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[gemini-code-assist]

Code Review

This pull request updates the documented default RocksDB block size from 64 KB to 32 KiB (or 32 KB) in the RocksDB overview and memory tuning guides. The reviewer provided valuable feedback to improve readability and consistency, suggesting a rephrasing of the block cache description in rocksdb-overview.md and recommending the use of 32KiB instead of 32KB in tune-tikv-memory-performance.md to align with standard TiKV configuration formats.

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[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #23271.