refactor: implement ConcatSource

[underfin]

Description

implement ConcatSource instead of concat_sourcemap.

Test Plan

Not need.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 64.51613% with 22 lines in your changes are missing coverage. Please review.

Project coverage is 78.63%. Comparing base (7ae8435) to head (c64261b).
Report is 3 commits behind head on main.

Files	Patch %	Lines
crates/rolldown_sourcemap/src/concat_sourcemap.rs	59.57%	19 Missing ⚠️
crates/rolldown/src/chunk/mod.rs	80.00%	3 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #611      +/-   ##
==========================================
- Coverage   78.95%   78.63%   -0.33%     
==========================================
  Files         142      142              
  Lines        6510     6599      +89     
==========================================
+ Hits         5140     5189      +49     
- Misses       1370     1410      +40     

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[hyf0]

@underfin I ran rust benchmark locally with this PR and get

Benchmarking rolldown benchmark/threejs-sourcemap: Collecting 20 samples in estimated 332.45 s (20 iterations)

This break benchmark action. Do you have time fix it?