Update npm dependencies; replace ajv with @sourcemeta/jsonschema

[glin]

Update npm dependencies to address CVEs:

• Update to eslint 9
• Replace ajv-cli (no longer maintained with unaddressed high CVEs) with https://github.com/sourcemeta/jsonschema
• Fix an unrelated test failure with some unescaped regex

[posit-snyk-bot]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scanner	Critical	High	Medium	Low	Total (0)
✅	Licenses	0	0	0	0	0 issues
✅	Open Source Security	0	0	0	0	0 issues

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