[Docs] Fix inline backticks in sparse and metric CN docs

[ghost]

Summary

• fix invalid inline single backticks in 22 Chinese API docs (pooling/conv functional + sparse/metric/optimizer)
• keep role/link/math syntax unchanged
• follow conservative boundary to avoid touching valid rst role/link forms

Test

• prek run --files <updated 22 docs>

[paddle-bot]

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[github-actions]

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• docs/api/paddle/metric/Metric_cn.rst: 点击预览
• docs/api/paddle/nn/functional/adaptive_avg_pool1d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/adaptive_max_pool1d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/avg_pool1d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/avg_pool2d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/avg_pool3d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/fractional_max_pool2d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/fractional_max_pool3d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/lp_pool1d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/lp_pool2d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/max_pool1d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/max_pool2d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/max_pool3d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/max_unpool1d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/max_unpool2d_cn.rst: 点击预览
• docs/api/paddle/nn/functional/max_unpool3d_cn.rst: 点击预览
• docs/api/paddle/optimizer/Adadelta_cn.rst: 点击预览
• docs/api/paddle/sparse/masked_matmul_cn.rst: 点击预览
• docs/api/paddle/sparse/matmul_cn.rst: 点击预览
• docs/api/paddle/sparse/mv_cn.rst: 点击预览
• docs/api/paddle/sparse/nn/functional/attention_cn.rst: 点击预览
• docs/api/paddle/sparse/sum_cn.rst: 点击预览