feat: print end status in watch mode

[nnecec]

I sometimes wonder if I've built done in watch mode, because it print nothing when built sucessfully.
 
Do we need to print some hint like these in watch mode?

> bunchee -w

Watching project /Users/nnecec/Github/bunchee...
📦 Build in: 1.956s
📦 Build in: 595.334ms
src/bundle.ts(25,3): error TS6133: 'getPackageMeta' is declared but its value is never read.
src/bundle.ts(70,64): error TS2304: Cannot find name 'pkg'.
src/bundle.ts(71,38): error TS2304: Cannot find name 'pkg'.
src/bundle.ts(73,38): error TS2304: Cannot find name 'pkg'.
src/bundle.ts(75,26): error TS2304: Cannot find name 'pkg'.
src/bundle.ts(153,40): error TS2304: Cannot find name 'pkg'.
src/bundle.ts(177,5): error TS18004: No value exists in scope for the shorthand property 'pkg'. Either declare one or provide an initializer.

📦 Build in: 652.215ms
📦 Build in: 512.592ms

[nnecec]

Ignore this feat if you don't think it's necessary, just my personal opinion.

[huozhi]

Thanks, this is a nice feature.
Can we polish the output to sth like

✓ Built in xxx ms

Without including the emoji and :

[nnecec]

Now it look like

> bunchee -w
Watching assets in /Users/nnecec/Github/bunchee...
✓ Build in 2875.94ms
src/bundle.ts(30,3): error TS6133: 'formatDuration' is declared but its value is never read.

✓ Build in 1541.16ms
✓ Build in 1727.21ms

[huozhi]

Looks good, can we add a test? Then I will merge later release this in a minor version. Thank you!

[huozhi]

I refactored a bit the code, to leverage the build jobs count instead of using another counter, since that one could be incorrect that it might reaches to 0 ealier