internal/driver: close saved profile files

[cuishuang]

Remote profiles are saved to an *os.File returned by newTempFile, but the file was not closed after Profile.Write returned.

This is mostly hidden for short-lived CLI invocations, but leaks file descriptors when pprof is used repeatedly from a long-lived process.

Close the saved profile file after writing, treat close failures as save failures, and only print the success message when both writing and closing succeed. Preserve the write error if both operations fail.

Add tests covering successful writes, write failures, close failures, and combined write and close failures.

Tests:

• ./test.sh

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.40%. Comparing base (4d45320) to head (c2eb7ac).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1022      +/-   ##
==========================================
+ Coverage   67.38%   67.40%   +0.02%     
==========================================
  Files          45       45              
  Lines        7846     7852       +6     
==========================================
+ Hits         5287     5293       +6     
  Misses       2115     2115              
  Partials      444      444              

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