fix(pgwire): fix cursor fetch for asyncpg

[bziobrowski]

Fixes #1897

Fixes cursor fetches from asyncpg code with:

• bind variables - asyncpg doesn't seem to specify type of bind variables in Bind message but uses those sent back by server in ParameterDescription
• Flush commands in between - Flush command shouldn't clear current state on server side but trigger processing pending messaged and pushing buffer content to client .

[ideoma]

[PR Coverage check]

😍 pass : 3 / 3 (100.00%)

file detail

	path	covered line	new line	coverage
🔵	io/questdb/cutlass/pgwire/PGConnectionContext.java	3	3	100.00%