Bump CometBFT to v0.38.21 (Tachyon patch)

[metalarm10]

Description

Updates CometBFT v0.38.19 → v0.38.21 to address CSA-2026-001 (Tachyon patch).

Reviewers checklist:

• Try to write more meaningful comments with clear actions to be taken.
• Nit-picking should be unblocking. Focus on core issues.

Authors checklist

• Provide a concise and meaningful description
• Review the code yourself first, before making the PR.
• Annotate your PR in places that require explanation.
• Think and try to split the PR to smaller PR if it is big.

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This change is 

[ysv]

@ysv reviewed 3 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @masihyeganeh, @miladz68, and @TxCorpi0x).

[TxCorpi0x]

@TxCorpi0x reviewed 7 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @masihyeganeh and @miladz68).