fix(types): match native manager return values

[OskarEichler]

Fixes

Align the internal NativeModules.VideoManager interface with the actual bridges:

• imperative commands return void, not promises
• save is optional because Android and Windows do not export it
• getCurrentPosition resolves a fractional JavaScript number rather than an Int32
• React tags consistently use Int32

The incorrect promise declarations could encourage awaiting values that are actually undefined, and the integer position type discarded the native APIs' sub-second contract.

Regression coverage

The v6 branch has no test suite (yarn test reports no test available). Verified with:

• YARN_NODE_LINKER=node-modules yarn prettier --check src/specs/NativeVideoManager.ts
• YARN_NODE_LINKER=node-modules yarn build
• YARN_NODE_LINKER=node-modules yarn lint
• React Doctor (100/100, no findings)
• git diff --check

Breaking changes

None for the public VideoRef API; this corrects the package-internal native-module declaration.