sqlparser: use integers instead of literals for Length/Precision

[vmg]

Description

As discussed with @dbussink, this is a potential fix for #15257

Dirkjan believes the aggregation lifting issue is scoped to the specific literals in CastExpr because it appears it's the only Expr that embeds Literals inside. I'm not 100% sure this covers all our bases, but I definitely agree that these length/precision fields should not be Literal, they should be stored directly as optional integers.

So here we go. The PR also includes some related cleanups for more optional integers in the sqlparser package.

cc @systay @frouioui @GuptaManan100

Related Issue(s)

• Aggregation Planner doesn't handle Literals properly  #15257

Checklist

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[GuptaManan100]

LGTM

[codecov]

Codecov Report

Attention: 18 lines in your changes are missing coverage. Please review.

Comparison is base (09c3d56) 67.44% compared to head (4af33b3) 67.47%.
Report is 11 commits behind head on main.

Files	Patch %	Lines
go/vt/vtgate/evalengine/expr_convert.go	88.23%	4 Missing ⚠️
go/vt/vtgate/evalengine/fn_time.go	0.00%	4 Missing ⚠️
go/vt/sqlparser/ast_format.go	40.00%	3 Missing ⚠️
go/vt/vtgate/evalengine/translate_convert.go	82.35%	3 Missing ⚠️
go/vt/vtgate/evalengine/format.go	60.00%	2 Missing ⚠️
go/vt/sqlparser/goyacc/goyacc.go	0.00%	1 Missing ⚠️
go/vt/vtgate/evalengine/expr_collate.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15256      +/-   ##
==========================================
+ Coverage   67.44%   67.47%   +0.02%     
==========================================
  Files        1560     1561       +1     
  Lines      193017   193186     +169     
==========================================
+ Hits       130180   130344     +164     
- Misses      62837    62842       +5     

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