docs: harmonize PR/issue refs in release notes

[FabianHofmann]

Harmonizing the PR/issue references in the release notes so they render consistently as clickable short-refs instead of a mix of bare URLs and inconsistent RST link forms.

Note

The following content was generated by AI.

Changes proposed in this Pull Request

• Convert bare GitHub URLs in the Upcoming Version and 0.8.0 sections to the canonical anonymous RST short-ref form `#NNN <url>`__ (renders as a clickable #NNN).
• Normalize single-underscore named references (`_) to anonymous double-underscore (`__). Labels like #580 and #776 appear more than once; named references with duplicate link text emit "duplicate target name" build warnings, anonymous references do not.
• Linkify the plain, unlinked #580 mentions.
• Fix a stray Markdown link ([here](...)) in the 0.1.4 notes that rendered literally in RST, converting it to an RST external link.

Documentation-only change; no code or behavior is affected.

Checklist

• AI-generated content is marked (see AGENTS.md).
• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[codspeed-hq]

Merging this PR will not alter performance

✅ 173 untouched benchmarks
⏩ 173 skipped benchmarks¹

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_{Comparing docs/harmonize-release-note-refs (aa79ebb) with master (e295723)}

Footnotes

1. 173 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩