perf: eagerly calculate source-map

[h-a-n-a]

Summary

Test Plan

No need.

Require Documentation?

• No
• Yes, the corresponding rspack-website PR is __

[h-a-n-a]

!bench

[rspack-bot]

📝 Benchmark detail: Open

name	base	current	%
10000_development-mode + exec	1.41 s ± 15 ms	1.62 s ± 14 ms	+14.81%
10000_development-mode_hmr + exec	957 ms ± 11 ms	1.13 s ± 9.5 ms	+18.55%
10000_production-mode + exec	3.4 s ± 43 ms	3.49 s ± 20 ms	+2.83%
threejs_development-mode_10x + exec	1.58 s ± 12 ms	2.13 s ± 17 ms	+35.24%
threejs_development-mode_10x_hmr + exec	967 ms ± 8 ms	1.43 s ± 5.6 ms	+48.40%
threejs_production-mode_10x + exec	5.64 s ± 18 ms	6.08 s ± 43 ms	+7.93%

Threshold exceeded: ["10000_development-mode + exec","10000_development-mode_hmr + exec","threejs_development-mode_10x + exec","threejs_development-mode_10x_hmr + exec","threejs_production-mode_10x + exec"]

[h-a-n-a]

This should be better done parallel in the rspack-sources itself. So I decide to close it.