feat: add fail-only option

[KoheiMatsuno99]

Summary

This PR adds a new -fail-only flag that filters tparse output to show only failed tests and packages.

Motivation

Closes #90

Example

With failures (filtered output)

  tparse % go test -json ./tests | go run main.go -fail-only
  ╭────────┬─────────┬───────────────────────────────────┬──────────────────────────────────╮
  │ Status │ Elapsed │               Test                │             Package              │
  ├────────┼─────────┼───────────────────────────────────┼──────────────────────────────────┤
  │  FAIL  │  0.01   │ TestFollow                        │ github.com/mfridman/tparse/tests │
  │  FAIL  │  0.01   │ TestFollow/follow_verbose         │ github.com/mfridman/tparse/tests │
  │  FAIL  │  0.00   │ TestFollow/follow_verbose/test_06 │ github.com/mfridman/tparse/tests │
  ╰────────┴─────────┴───────────────────────────────────┴──────────────────────────────────╯
  ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
  ┃   FAIL  package: github.com/mfridman/tparse/tests   ┃
  ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛

  --- FAIL: TestFollow (0.01s)
  --- FAIL: TestFollow/follow_verbose (0.01s)
  --- FAIL: TestFollow/follow_verbose/test_06 (0.00s)

      follow_test.go:52:
                  Error Trace:    /Users/koheimatsuno/tparse/tests/follow_test.go:52
                  Error:          Not equal:
                                  expected: 2
                                  actual  : 1
                  Test:           TestFollow/follow_verbose/test_06

  ╭────────┬─────────┬──────────────────────────────────┬───────┬──────┬──────┬──────╮
  │ Status │ Elapsed │             Package              │ Cover │ Pass │ Fail │ Skip │
  ├────────┼─────────┼──────────────────────────────────┼───────┼──────┼──────┼──────┤
  │  FAIL  │  0.27s  │ github.com/mfridman/tparse/tests │  --   │ 142  │  3   │  0   │
  ╰────────┴─────────┴──────────────────────────────────┴───────┴──────┴──────┴──────╯
  exit status 1

Flag precedence warning

• When -fail-only is combined with -pass, -skip, or -all, it takes precedence and shows a warning.
• This design choice reflects the explicit user intent: if someone specifies -fail-only, they want to see only failures regardless of other flags.

  tparse % go test -json ./tests | go run main.go -fail-only -all
  warning: -fail-only takes precedence over -pass, -skip, and -all flags
  ╭────────┬─────────┬───────────────────────────────────┬──────────────────────────────────╮
  │ Status │ Elapsed │               Test                │             Package              │
  ├────────┼─────────┼───────────────────────────────────┼──────────────────────────────────┤
  │  FAIL  │  0.01   │ TestFollow                        │ github.com/mfridman/tparse/tests │
  │  FAIL  │  0.01   │ TestFollow/follow_verbose         │ github.com/mfridman/tparse/tests │
  │  FAIL  │  0.00   │ TestFollow/follow_verbose/test_06 │ github.com/mfridman/tparse/tests │
  ╰────────┴─────────┴───────────────────────────────────┴──────────────────────────────────╯
  ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
  ┃   FAIL  package: github.com/mfridman/tparse/tests   ┃
  ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛

  --- FAIL: TestFollow (0.01s)
  --- FAIL: TestFollow/follow_verbose (0.01s)
  --- FAIL: TestFollow/follow_verbose/test_06 (0.00s)

      follow_test.go:52:
                  Error Trace:    /Users/koheimatsuno/tparse/tests/follow_test.go:52
                  Error:          Not equal:
                                  expected: 2
                                  actual  : 1
                  Test:           TestFollow/follow_verbose/test_06

  ╭────────┬─────────┬──────────────────────────────────┬───────┬──────┬──────┬──────╮
  │ Status │ Elapsed │             Package              │ Cover │ Pass │ Fail │ Skip │
  ├────────┼─────────┼──────────────────────────────────┼───────┼──────┼──────┼──────┤
  │  FAIL  │  0.27s  │ github.com/mfridman/tparse/tests │  --   │ 142  │  3   │  0   │
  ╰────────┴─────────┴──────────────────────────────────┴───────┴──────┴──────┴──────╯
  exit status 1

All tests passing

  tparse % go test -json ./tests | go run main.go -fail-only
  No tests failed.

Testing

Added TestFailOnly with golden file tests covering:

• Mixed success/failure scenario (shows only failures)
• All tests passing scenario (shows "No tests failed.")