fix(provider): improve string truncation handling in TruncateString

[VolodymyrBg]

Description

This PR addresses inefficiencies and potential bugs in the TruncateString function located in x/ccv/provider/types/msg.go. The previous implementation had several issues:

• It used character-by-character string concatenation, resulting in O(n²) time complexity
• It didn't properly handle Unicode characters, potentially cutting multi-byte characters in the middle
• It lacked proper boundary checks for edge cases
  The improved implementation:
• Uses standard string slicing for better performance (O(1) vs O(n²))
• Adds proper UTF-8 validation to prevent cutting Unicode characters in the middle
• Implements boundary checks to ensure safe operation with large strings
• Adds handling for edge cases when maxLength reaches zero
  These changes improve both performance and correctness, particularly when handling non-ASCII strings that contain multi-byte Unicode characters.

Closes: #XXXX

Author Checklist

I have...
[x] Included the correct type prefix in the PR title
[ ] Added ! to the type prefix if the change is state-machine breaking
[x] Confirmed this PR does not introduce changes requiring state migrations, OR migration code has been added to consumer and/or provider modules
[x] Targeted the correct branch (see PR Targeting)
[ ] Provided a link to the relevant issue or specification
[x] Followed the guidelines for building SDK modules
[x] Included the necessary unit and integration tests
[x] Added a changelog entry to CHANGELOG.md
[x] Included comments for documenting Go code
[x] Updated the relevant documentation or specification
[x] Reviewed "Files changed" and left comments if necessary
[x] Confirmed all CI checks have passed
[ ] If this PR is library API breaking, bump the go.mod version string of the repo, and follow through on a new major release
Reviewers Checklist
All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.
I have...
[ ] confirmed the correct type prefix in the PR title
[ ] confirmed ! the type prefix if the change is state-machine breaking
[ ] confirmed this PR does not introduce changes requiring state migrations, OR confirmed migration code has been added to consumer and/or provider modules
[ ] confirmed all author checklist items have been addressed
[ ] reviewed state machine logic
[ ] reviewed API design and naming
[ ] reviewed documentation is accurate
[ ] reviewed tests and test coverage