chore(lint): Enable Pyflakes rules across all packages

[ayushiahjolia]

Issue #, if available: #479

Description of changes:
Enables the Pyflakes (F) rule category in ruff across all packages. reviously only TID252 (ban relative imports) was enforced, meaning unused imports, undefined names, and unused variables went undetected.

Testing -

• ci-checks.sh passes (tests, coverage, typecheck, fmt for all packages)
• ruff check --select F,TID252 reports zero violations

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[zhongkechen]

Unused imports in Python might be actually used because the imported symbols may not be used in the current module, instead be used by other modules importing this module

[ayushiahjolia]

Hmm I relied on tests to verfify this, I found one variable which was used at runtime, but no other issues.

[yaythomas]

d238353 "update ruff config" added: +select = ["TID252"] # Enforce absolute imports (ban relative imports)

This is the regression point. Adding TID252 as the sole entry overrode the default and silently switched off F (and the E4/E7/E9 subset). From here, unused imports/vars accumulated undetected.

The PR could optionally also restore E4/E7/E9 (the rest of the old default) via select = ["E4","E7","E9","F","TID252"], since those were dropped in the same commit.

And a minor pre-existing inconsistency: the testing package sets preview = false while the others set preview = true. Not necessarily in scope for this PR :-)