Upgrade core SDK → Jackson 3

## Describe the proposal

# Change Proposal: Migrate core Java SDK from Jackson 2 → Jackson 3

## Summary
Move `dapr-sdk` (and `sdk-actors`, `sdk-springboot`, `durabletask-client`) off Jackson 2 (`com.fasterxml.jackson`) onto Jackson 3 (`tools.jackson`), so the whole SDK uses a single Jackson line. **Separate PR from the Spring Boot 4 migration** — not a prerequisite for it.

## Motivation
- SB4 / Spring AI 2.0 already use Jackson 3; core SDK still uses Jackson 2. Both currently coexist on the classpath (works, but two Jackson lines).
- Long-term: single dependency, lighter classpath, aligned with the rest of the ecosystem.

## Not urgent
Jackson 2 (2.21.2) is still BOM-managed by Spring Boot 4 and actively maintained upstream. Nothing forces this now. It's cleanup, not a fix.

## Scope (what changes)
- **Annotations (47 uses): no change.** Jackson 3 keeps `@JsonProperty` etc. in `com.fasterxml.jackson.annotation`. This is the majority of usage — it rides along free.
- **`ObjectMapper` construction (~13 sites)**: `new ObjectMapper().configure(...)` → `JsonMapper.builder()…build()` (mapper is now immutable). Sites: `ObjectSerializer`, `AbstractDaprClient`, `DaprHttp`, `CloudEvent`, `Filter` (sdk); `DaprClientImpl`, `DaprStateAsyncProvider` (sdk-actors); `DaprBeanPostProcessor` (sdk-springboot); `JacksonDataConverter` (durabletask).
- **2 custom (de)serializers**: `CloudEvent`, `StateOptions` — extend `JsonSerializer`/`JsonDeserializer`, which move to `tools.jackson.databind`.
- **Exceptions**: Jackson 3 read/write exceptions are now unchecked → drop `throws IOException`/`JsonProcessingException` where they were Jackson-only.

## Breaking changes (public API — small but real)
1. `CustomizableObjectSerializer(ObjectMapper)` constructor + `getObjectMapper()` — parameter/return type changes package (`com.fasterxml…` → `tools.jackson…`).
2. `ObjectSerializer.parseNode(byte[]) : JsonNode` — `JsonNode` changes package.

Anyone passing a custom mapper or calling `parseNode` breaks at source + binary level. The main serializer SPI (`DaprObjectSerializer`) is Jackson-free, so most users are unaffected.

## Plan
1. Bump core modules to `tools.jackson` (Jackson 3 BOM already on the SB4 dependency tree).
2. Rewrite the ~13 mapper sites + 2 custom serializers; clean up now-unchecked exceptions.
3. Update `CustomizableObjectSerializer` / `parseNode` signatures.
4. Document the two breaks in the changelog.

## Recommendation
Land it as its own PR with a changelog note, sequenced **after** the SB4 cutover merges. Because it touches public signatures, treat it as a breaking change for release-versioning purposes.