Update changelog with latest 6.5 chnages

[masih]

Backported from the release branch

[cursor]

PR Summary

Low Risk
Documentation-only changelog update with no code, config, or state-machine impact.

Overview
Updates CHANGELOG.md under v6.5 by inserting seven release/backport entries at the top of the sei-chain list (newest first), including v6.5.1, v6.5.0 cut, RC prep bumps, giga iterator fix (#3563), EIP-1559 effective gas price on receipts, and pre-v6.5 debug trace decoding.

Also adds a blank line before the v6.4 section. No application or runtime code is modified—documentation only, backported from release/v6.5.

^{Reviewed by Cursor Bugbot for commit 2c56e26. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Jun 10, 2026, 9:13 AM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.32%. Comparing base (ba465c7) to head (2c56e26).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3571      +/-   ##
==========================================
- Coverage   59.16%   58.32%   -0.85%     
==========================================
  Files        2226     2152      -74     
  Lines      183561   175014    -8547     
==========================================
- Hits       108613   102080    -6533     
+ Misses      65167    63859    -1308     
+ Partials     9781     9075     -706     

Flag	Coverage Δ
sei-db	70.41% <ø> (ø)
sei-db-state-db	?

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see 74 files with indirect coverage changes

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