Type renameProperties generically to eliminate implicit any in utils (toward #133)

[Epi-1120]

Purpose

Incremental step toward #133 — eliminate implicit and explicit any from src/. Continuing the small-PR approach from #138, this PR narrows the scope to src/utils/index.ts only.

Under tsc --noImplicitAny --strictNullChecks, both parameters of renameProperties were implicitly typed as any:

src/utils/index.ts(1,34): error TS7006: Parameter 'features' implicitly has an 'any' type.
src/utils/index.ts(2,17): error TS7006: Parameter 'ft' implicitly has an 'any' type.

What this PR does

• Introduces a local FeatureWithBegin type capturing the only shape assumption the function body actually makes about its input (an optional begin field of type string | number).
• Makes renameProperties generic in T extends FeatureWithBegin, so every other property on the caller's feature shape is preserved on the returned objects. No downstream type information is lost.

What this PR does not do

• No runtime changes. The function body is byte-for-byte identical.
• No changes to callers (src/adapters/feature-adapter.ts, src/adapters/proteomics-adapter.ts). Both still pass untyped data in for now; that is left to a follow-up PR that tightens the adapters themselves.
• No changes to tsconfig.json / ESLint config yet.

Verification

tsc --noImplicitAny --strictNullChecks   # src/utils: 0 errors (was 2)
eslint src/utils/index.ts                # clean
vite build                               # OK
vitest run                               # 4 files / 60 tests, all pass

Follow-ups (separate PRs)

• src/adapters/** implicit-any cleanup (largest cluster)
• src/tooltips/** implicit-any cleanup
• src/protvista-uniprot.ts — the central adapter dispatch map (Record<string, (...args: any[]) => any>) and the NightingaleEvent detail shape
• Closing PR: enable noImplicitAny: true, strictNullChecks: true, and @typescript-eslint/no-explicit-any: 'error' once the tree is clean

Testing checklist

• I have tested the changes locally (vite build, vitest run)
• The change has no runtime impact (types only)
• The diff is minimal and scoped to a single file