feat: support multiline SQL input in obclient #<573>

[e-gonzalezz]

What problem were solved in this pull request?

Previously, obclient did not support multi-line SQL input.
When users entered a statement that spanned multiple lines (e.g., CREATE TABLE), the client failed to parse it and returned an error.

Issue Number: close #573

What is changed and how it works?

Enhanced the client input handling logic to buffer input until a terminating semicolon (;) is received.
Modified the prompt to match MySQL-style continuation (->) for multi-line queries.
Now, users can input SQL statements across multiple lines, and the client will execute them only when complete.

Example before:

miniob > create table t(
SQL_SYNTAX > Failed to parse sql

Example after:

miniob > create table t(
-> a int,
-> b int);
SUCCESS

Other information

Tested with CREATE TABLE both single-line and multi-line.

[CLAassistant]

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