fix(snippets): number terminal snippets from their first line

[Eljees]

Fixes #283.

--show-uncovered prints each snippet with line numbers, but in the terminal they always started at 0001, while the HTML and Markdown reports number the same snippet from its real first line. Snippet.terminal() passes linenostart to Pygments' TerminalFormatter, and that formatter ignores the option (it is only honoured by the HTML formatter). Checked with the current Pygments, 2.21.0:

>>> pygments.highlight("a = 1\nb = 2\n", PythonLexer(),
...     TerminalFormatter(linenos=True, colorscheme=None, linenostart=217))
'0001: a = 1\n0002: b = 2\n0003: \n'

This renders the snippet with TerminalFormatter but without line numbers, and adds them in terminal() in the same %04d: form, starting at the snippet's first line. The output is otherwise unchanged, including the trailing numbered empty line that show_uncovered_lines_console.txt expects, so the existing integration test passes as is.

Tests: test_terminal_numbers_lines_from_start_line builds a snippet that starts at line 217 and checks that its lines are 0217:, 0218:, 0219:. On main it fails:

AssertionError: assert ['0001: Line ...03: Line 219'] == ['0217: Line ...19: Line 219']

A second test pins the numbering for a snippet at the top of the file.

Full suite in a clean container: 389 passed with the change and 387 on main. The same 18 TestDiffQualityIntegration tests fail on both, because that environment does not have the quality tools (pylint, pyflakes and so on) installed.

[Bachmann1234]

Thanks for the fix!