Fix correctness, performance, and polish issues in timeline rendering

[pushpalroy]

Summary

Three-phase cleanup of the :jetlime library (commonMain). Public API is unchanged.

Critical correctness (f2a3324)

• JetLimeStyle.arrangement is now an internal val constructor param; alignment() returns a new instance instead of mutating this. Prevents silent corruption when a single style instance is shared between a Column and a Row.
• Removed keyless remember { ... } around lineVerticalAlignment / lineHorizontalAlignment — the cached values never updated when the caller swapped the style.
• Deleted a duplicate drawLine call for CENTER point placement (vertical) that painted the same segment twice — visible under alpha / dashed brushes.

Performance / recomposition (6227ddf)

• calculateRadiusAnimFactor only calls rememberInfiniteTransition when pointAnimation != null. Previously every item registered an unused infinite transition with the Recomposer.
• JetLimeColumn / JetLimeRow remember(style) { style.alignment(...) } so the value provided to LocalJetLimeStyle is stable across recompositions and consumers can skip.
• JetLimeExtendedEvent no longer uses BoxWithConstraints or a sibling Canvas. The timeline X offset is published from measure into a MutableFloatState read by a Modifier.drawBehind on the Layout itself, so the state write only invalidates the draw phase instead of triggering recomposition of a sibling composable.

Polish (e5edc1c)

• EventPosition.isNotStart() compares against the START singleton instead of the literal string "Start", matching isNotEnd().
• LocalJetLimeStyle switched to staticCompositionLocalOf — the style is now stable across recompositions and read by every item.

Test plan

• ./gradlew :jetlime:compileDebugKotlinAndroid — clean build
• ./gradlew :jetlime:spotlessCheck — passes
• ./gradlew :jetlime:connectedAndroidTest — run existing instrumented suite (Column/Row/RTL tests) on a device / emulator before merge
• Visual spot-check sample app for all three PointPlacement variants in both LTR and RTL

Deferred to a future major version

Tracked separately — all require source or binary breaks:

• JetLimeEventStyle.position / pointPlacement var → val
• ItemsList backed by ImmutableList<T>
• EventPointType.equals semantics over Painter
• EventPosition → enum class
• Sample / docs to remember eventStyle(...) per item

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