chore(release): bump version to 6.2.1

[dwolfson]

Bumps the version to 6.2.1 in pyproject.toml and uv.lock. PyPI returns 404 for 6.2.1, so the version is free.

Changes since 6.2.0:

• fix(omvs): by-name type filter reaches Egeria; read nestedSolutionComponents (ISSUE-131, ISSUE-133) #439: by-name searches send the type filter again (ISSUE-131); solution component children read from nestedSolutionComponents (ISSUE-133)
• chore(deps): Bump multidict from 6.7.1 to 6.9.1 #437: multidict 6.7.1 to 6.9.1, which fixes Dependabot alert Experimenting with MCP #133
• chore(deps): bump github/codeql-action init+analyze to 4.38.2 together; group in Dependabot #441: CodeQL action bumped to 4.38.2 for both steps, now grouped in Dependabot
• chore(gitignore): ignore pyegeria/http-clients/ #440: .gitignore ignores pyegeria/http-clients/
• docs(issues): log ISSUE-128..134, verify 127/129/131 against Egeria source #438: PYEGERIA_ISSUES.md adds ISSUE-128 to ISSUE-134

uv lock also added sys_platform markers to three dependency entries (h11, truststore, ptyprocess). This comes from a newer uv and changes no versions.

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