chore: Add JSR publishing configuration and instructions

[ysknsid25]

I prepared setting for JSR. if this pull request merged, I'll do below next actions.

Next Actions

• write JSDoc and module doc for enhansing JSR Score.
• write GitHub Actions for sync version no between package.json and jsr.json.

jsr publish --dry-run Result

Checking for slow types in the public API...
Simulating publish of @unjs/ofetch@2.0.0-alpha.3 with files:
   /unjs/ofetch/LICENSE (1.05KB)
   /unjs/ofetch/README.md (11.09KB)
   /unjs/ofetch/jsr.json (332B)
   /unjs/ofetch/src/base.ts (56B)
   /unjs/ofetch/src/error.ts (1.84KB)
   /unjs/ofetch/src/fetch.ts (8.47KB)
   /unjs/ofetch/src/index.ts (498B)
   /unjs/ofetch/src/types.ts (3.96KB)
   /unjs/ofetch/src/utils.ts (3.54KB)
   /unjs/ofetch/src/utils.url.ts (2.92KB)
Success Dry run complete

Completed in 513ms

About publish.yml

For enhansing JSR Score, We should publish from GHA. (FYI)

So I prepared publish.yml but I didn't verify in GHA. I used Hono as a reference.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.55%. Comparing base (27996d3) to head (5aad0e7).
⚠️ Report is 100 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #528       +/-   ##
===========================================
+ Coverage   56.86%   85.55%   +28.68%     
===========================================
  Files          16        5       -11     
  Lines         728      263      -465     
  Branches      113      133       +20     
===========================================
- Hits          414      225      -189     
+ Misses        303       33      -270     
+ Partials       11        5        -6     

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