feat: #2576 Added typeadapter to read and write Instant values.

[ablx]

This PR adds a default TypeAdapter to the Spanner Mapping Context, enabling seamless mapping of java.time.Instant. Consequently, the need to include --add-opens java.base/java.time=ALL-UNNAMED in JVM arguments is eliminated.

Solves #2576

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[conventional-commit-lint-gcf]

🤖 I detect that the PR title and the commit message differ and there's only one commit. To use the PR title for the commit history, you can use Github's automerge feature with squashing, or use automerge label. Good luck human!

-- conventional-commit-lint bot
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[sonarcloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
81.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[burkedavison]

Retargeted this PR to new branch feat/2576-instant-typeadapter. Will need to merge it here and open a new PR into main to ensure integration tests are triggered.