Update error message for cells with too much text

[ttsukagoshi]

This pull request resolves #75 by informing the user of a rough estimate of the optimal text length in the error message.

Original Message

[SheetsL] Cell content is too long. Please consider splitting the content into multiple cells:
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Updated Message

[SheetsL] Cell content length exceeds Google's limits. Please consider splitting the content into multiple cells. The following is the estimated maximum length of the cell in question:
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis

Please note that this is a rough estimate and that the actual acceptable text length might differ slightly.

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🔴	Statements	58.99% (-0.76% 🔻)	279/473
🟢	Branches	100%	31/31
🟡	Functions	69.23%	9/13
🔴	Lines	58.99% (-0.76% 🔻)	279/473

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🔴	sheetsl.ts	58.99% (-0.76% 🔻)	100%	69.23%	58.99% (-0.76% 🔻)

Test suite run success

21 tests passing in 7 suites.

Report generated by 🧪jest coverage report action from fcfbf78