refactor(utils): consolidate string and option handling

[lxy-9602]

Purpose

This PR consolidates duplicated string and option handling into the common utility classes.

The main changes are:

• Align StringUtils edge-case behavior with the corresponding Java implementation, including replace, trim, and starts-with operations.
• Add ASCII-based case conversion and case-insensitive comparison helpers.
• Add OptionsUtils::GetNonEmptyValueFromMap and improve prefixed option extraction.
• Replace duplicated string and option handling across REST, filesystem, schema validation, variant, and system-table code.
• Reuse SpecialFields::CompleteSequenceAndValueKindField when constructing the postpone-bucket write schema.
• Remove redundant parquet.read.enable-pre-buffer=false injection from compaction paths. Compaction always enables framework prefetch, which already disables Parquet pre-buffering, so mutating the format options is unnecessary.

Tests

Added or updated unit coverage for:

• StringUtils edge cases and case-insensitive comparison.
• OptionsUtils non-empty values and prefixed option extraction.
• Case-insensitive local filesystem schemes.
• Case-insensitive Parquet format validation.
• Sequence snapshot property parsing.

API and Format

Documentation

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[zjw1111]

+1

[SteNicholas]

LGTM.