Rework migration code generation

[sebastian-ederer]

Description

Before, migration files were spammed with .Sql() calls containing the raw SQL strings. This did not adhere to a clear separation of concerns and the migration files did not look clean. Now the migration files look a lot cleaner and we have a clearer SoC in the internal code. This also makes the code more maintanable as you only have one (and not two) locations where you need to maintain the raw SQL that will be executed.

Also, after refactoring renaming tables or columns is being handled better.

Type of Change

• Bug fix (non-breaking change adressing an issue)
• New feature (non-breaking change adding functionality)
• Refactoring
• Documentation
• CI / build / tooling
• Breaking change (fix or feature causing existing functionality to change)

Test Plan

• Unit tests added/updated
• Integration tests added/updated (Testcontainers)
• Existing tests pass (dotnet test)

Checklist

• Code follows the project's coding styles and guidelines
• I have updated the documentation accordingly
• I have added tests to cover my changes
• No new compiler warnings introduced
• Public API changes have XML documentation

[codecov]

Codecov Report

❌ Patch coverage is 97.88807% with 20 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ftdb/Generators/ContinuousAggregateSqlGenerator.cs	54.54%	0 Missing and 5 partials ⚠️
...Internals/Features/Hypertables/HypertableDiffer.cs	88.09%	2 Missing and 3 partials ⚠️
...n/Generators/ContinuousAggregateCSharpGenerator.cs	96.10%	0 Missing and 3 partials ⚠️
...tensions/ContinuousAggregateMigrationExtensions.cs	95.55%	0 Missing and 2 partials ⚠️
src/Eftdb/Generators/ReorderPolicySqlGenerator.cs	98.46%	0 Missing and 1 partial ⚠️
...rc/Eftdb/Generators/RetentionPolicySqlGenerator.cs	98.48%	0 Missing and 1 partial ⚠️
...ls/Features/ReorderPolicies/ReorderPolicyDiffer.cs	94.44%	0 Missing and 1 partial ⚠️
.../Eftdb/Internals/TimescaleMigrationsModelDiffer.cs	98.07%	0 Missing and 1 partial ⚠️
...onExtensions/RetentionPolicyMigrationExtensions.cs	97.91%	0 Missing and 1 partial ⚠️

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