feat(formatters): Add TAP (Test Anything Protocol) formatter

[juvistr]

Summary

Add TAP v13 output formatter for broad CI/CD tool compatibility.

Motivation

• Universal format: Supported by many CI tools
• Simple parsing: Line-based, easy to process
• Jenkins/legacy CI: TAP plugins widely available

Acceptance Criteria

• `draftspec run --format tap` outputs TAP format
• TAP v13 compliant output
• Includes diagnostics for failures
• Supports TODO/SKIP directives
• Tests added
• Documentation updated

Example Output

TAP version 13
1..47
ok 1 - UserService > CreateAsync > creates a user
ok 2 - UserService > CreateAsync > validates email
not ok 3 - UserService > CreateAsync > sends welcome email
  ---
  message: Expected email to be sent
  severity: fail
  at:
    file: UserService.spec.csx
    line: 45
  ...
ok 4 - UserService > GetAsync > returns user # SKIP temporarily disabled
ok 5 - UserService > DeleteAsync > removes user # TODO not implemented

Implementation Notes

• Create TapFormatter : IFormatter
• Register in FormatterRegistry
• Simple line-based output, minimal dependencies

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