fix: consume Matplotlib format markers

[RoboX2020]

The compact-format parser recognizes a marker but leaves it in working_fmt, so valid strings such as 'o', 'ro--', 'g^:' and '-.b*' raise ValueError as unrecognized components.

Remove the matched marker once, like the color and linestyle, before checking for leftover characters. Invalid duplicate markers and unmatched characters still raise.

Added nine checks covering the documented combined formats, a marker alone, tuple input, keyword precedence, and invalid leftovers. Six fail on the original implementation. The valid-format tests also create a Matplotlib line and check its marker.

Validation on Python 3.11:

• New tests: 9 passed on OpenCV 4.12.0.88 and 5.0.0.93.
• Full OpenCV 5 suite: 968 passed, 97 skipped, 5 subtests passed.
• Test file passes ruff and black.
• Inspected a headless render of the three combined formats: red circles/dashes, green triangles/dots, and blue stars/dash-dot lines.

Full suite on OpenCV 4 and a desktop GUI were not run. This is a one-line production fix, not an extension of the accepted format syntax.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 4 complexity · 0 duplication

Metric	Results
Complexity	4
Duplication	0

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