fix #620: [FR] Improve handling of 'siècle' template

[lasconic]

• Fixes [FR] Improve handling of 'siècle' template #620
• Tests added/updated.
• ./check.sh run and eventual issues fixed.
• Updated CONTRIBUTORS.md, if not already done in the past.

[sourcery-ai]

Sourcery Code Quality Report

❌  Merging this PR will decrease code quality in the affected files by 0.12%.

Quality metrics	Before	After	Change
Complexity	16.43 🙂	16.31 🙂	-0.12 👍
Method Length	81.28 🙂	82.16 🙂	0.88 👎
Working memory	9.73 🙂	9.82 🙂	0.09 👎
Quality	56.54% 🙂	56.42% 🙂	-0.12% 👎

Other metrics	Before	After	Change
Lines	650	659	9

Changed files	Quality Before	Quality After	Quality Change
wikidict/lang/fr/template_handlers.py	56.54% 🙂	56.42% 🙂	-0.12% 👎

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
wikidict/lang/fr/template_handlers.py	render_compose_de	51 ⛔	490 ⛔	15 😞	12.05% ⛔	Refactor to reduce nesting. Try splitting into smaller methods. Extract out complex expressions
wikidict/lang/fr/template_handlers.py	render_etyl	17 🙂	161 😞	10 😞	46.13% 😞	Try splitting into smaller methods. Extract out complex expressions
wikidict/lang/fr/template_handlers.py	render_mot_valise	13 🙂	126 😞	10 😞	53.27% 🙂	Try splitting into smaller methods. Extract out complex expressions
wikidict/lang/fr/template_handlers.py	render_cit_ref	10 🙂	169 😞	8 🙂	55.58% 🙂	Try splitting into smaller methods
wikidict/lang/fr/template_handlers.py	render_agglutination	12 🙂	102 🙂	10 😞	57.22% 🙂	Extract out complex expressions

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• 😞 poor
• ⛔ very poor

The 👍 and 👎 indicate whether the quality has improved or gotten worse with this pull request.

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