Use newly added panicking_add/panicking_sub for Timestamp math (backport #2098)

[mergify]

---

This is an automatic backport of pull request #2098 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 547efed has failed:

On branch mergify/bp/release/2.0/pr-2098
Your branch is up to date with 'origin/release/2.0'.

You are currently cherry-picking commit 547efeda0.
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Changes to be committed:
	modified:   packages/std/src/math/uint128.rs
	modified:   packages/std/src/math/uint256.rs
	modified:   packages/std/src/math/uint512.rs
	modified:   packages/std/src/math/uint64.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

Cherry-pick of 242cc1f has failed:

On branch mergify/bp/release/2.0/pr-2098
Your branch is ahead of 'origin/release/2.0' by 1 commit.
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You are currently cherry-picking commit 242cc1ffc.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   packages/std/src/timestamp.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

Cherry-pick of a74aba0 has failed:

On branch mergify/bp/release/2.0/pr-2098
Your branch is ahead of 'origin/release/2.0' by 2 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit a74aba0ef.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   packages/std/src/math/uint128.rs
	modified:   packages/std/src/math/uint256.rs
	modified:   packages/std/src/math/uint512.rs
	modified:   packages/std/src/math/uint64.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

Cherry-pick of b265b33 has failed:

On branch mergify/bp/release/2.0/pr-2098
Your branch is ahead of 'origin/release/2.0' by 4 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit b265b33c7.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   packages/std/src/timestamp.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

Cherry-pick of 198001e has failed:

On branch mergify/bp/release/2.0/pr-2098
Your branch is ahead of 'origin/release/2.0' by 5 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 198001e03.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CHANGELOG.md

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally