Fix: Add missing links to v2.1.0 release notes

[alexdewar]

Description

I spotted a few places where there were links for issues/PRs without an entry at the bottom of the file.

Type of change

• Bug fix (non-breaking change to fix an issue)
• New feature (non-breaking change to add functionality)
• Refactoring (non-breaking, non-functional change to improve maintainability)
• Optimization (non-breaking change to speed up the code)
• Breaking change (whatever its nature)
• Documentation (improve or add documentation)

Key checklist

• All tests pass: $ cargo test
• The documentation builds and looks OK: $ cargo doc
• Update release notes for the latest release if this PR adds a new feature or fixes a bug
  present in the previous release

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.74%. Comparing base (656eb32) to head (921f368).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1231   +/-   ##
=======================================
  Coverage   89.74%   89.74%           
=======================================
  Files          57       57           
  Lines        8195     8195           
  Branches     8195     8195           
=======================================
  Hits         7355     7355           
  Misses        544      544           
  Partials      296      296           

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[Copilot]

Pull request overview

Adds missing PR link-reference definitions to the v2.1.0 release notes so all inline [#NNNN] references resolve correctly when rendered.

Changes:

• Added link definitions for [#1110], [#1168], [#1170], and [#1205] in docs/release_notes/v2.1.0.md.

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[tsmbland]

Oops! That's weird, I added most of these in d812a06 but seem to have accidentally deleted them in 99fcd86. Thanks for checking!

[tsmbland]

#1168 is actually an issue rather than a PR, but that link will redirect so all good

[alexdewar]

Cool. Let's make this release!