Map.memoizedEncodePlans concurrent map writes (v5.7.2)

Describe the bug
When using a simple protocol and concurrent queries, a panic occurs with the error concurrent map writes in the memoizedEncodePlans function in the pgtype.Map module.

fatal error: concurrent map writes
...
github.com/jackc/pgx/v5/pgtype.(*Map).planEncodeDepth(0xc01173e5b0, 0x0, 0x0, {0x3aeda0, 0x648cfc0}, 0x0)
        /-S/vendor/github.com/jackc/pgx/v5/pgtype/pgtype.go:1254 +0x206 fp=0xc00cd08b08 sp=0xc00cd08a58 pc=0x3ef3bc6
github.com/jackc/pgx/v5/pgtype.(*Map).PlanEncode(...)
        /-S/vendor/github.com/jackc/pgx/v5/pgtype/pgtype.go:1234
github.com/jackc/pgx/v5/pgtype.(*Map).Encode(0xc01173e5b0, 0x0, 0x0, {0x3aeda0, 0x648cfc0}, {0x6488500, 0x0, 0x0})
        /-S/vendor/github.com/jackc/pgx/v5/pgtype/pgtype.go:2001 +0x12d fp=0xc00cd08b58 sp=0xc00cd08b08 pc=0x3ef99ed
github.com/jackc/pgx/v5.convertSimpleArgument(0x4c8380?, {0x3aeda0?, 0x648cfc0?})
        /-S/vendor/github.com/jackc/pgx/v5/values.go:17 +0x34 fp=0xc00cd08ba0 sp=0xc00cd08b58 pc=0x3fe8e14
github.com/jackc/pgx/v5.(*Conn).sanitizeForSimpleQuery(0xc014d0e900, {0xc021f80340, 0x185}, {0xc01aa19190, 0x1, 0xc01aa19190?})
        /-S/vendor/github.com/jackc/pgx/v5/conn.go:1244 +0x166 fp=0xc00cd08bf8 sp=0xc00cd08ba0 pc=0x3fdfba6
github.com/jackc/pgx/v5.(*Conn).Query(0xc014d0e900, {0x121c170?, 0xc044094230?}, {0xc021f80340, 0x185}, {0xc01aa19180, 0x2, 0x2})
        /-S/vendor/github.com/jackc/pgx/v5/conn.go:838 +0xbab fp=0xc00cd08de0 sp=0xc00cd08bf8 pc=0x3fdc06b
github.com/jackc/pgx/v5/stdlib.(*Conn).QueryContext(0xc01bb55e40, {0x121c170, 0xc044094230}, {0xc021f80340, 0x185}, {0xc03d1b9f80, 0x1, 0x5f32600?})
        /-S/vendor/github.com/jackc/pgx/v5/stdlib/sql.go:493 +0x32d fp=0xc00cd08ed0 sp=0xc00cd08de0 pc=0x40223ed
...

Expected behavior

No concurrent map writes panic should occur.

Actual behavior

A panic with the concurrent map writes error occurs when executing concurrent queries, indicating an attempt to write to the map simultaneously.

Version

Go: 1.22.5
pgx: v5.7.2

Additional context

Part of the core dump:

(dlv) bt
 0  0x0000000002fd1ca1 in runtime.raise
    at /-S/contrib/go/_std_1.22/src/runtime/sys_linux_amd64.s:154
 1  0x0000000002fb1805 in runtime.dieFromSignal
    at /-S/contrib/go/_std_1.22/src/runtime/signal_unix.go:923
 2  0x0000000002fb1f06 in runtime.sigfwdgo
    at /-S/contrib/go/_std_1.22/src/runtime/signal_unix.go:1128
 3  0x0000000002fb0425 in runtime.sigtrampgo
    at /-S/contrib/go/_std_1.22/src/runtime/signal_unix.go:432
 4  0x0000000002fd1ca1 in runtime.raise
    at /-S/contrib/go/_std_1.22/src/runtime/sys_linux_amd64.s:153
 5  0x0000000002fb1805 in runtime.dieFromSignal
    at /-S/contrib/go/_std_1.22/src/runtime/signal_unix.go:923
 6  0x0000000002f99c3a in runtime.crash
    at /-S/contrib/go/_std_1.22/src/runtime/signal_unix.go:1005
 7  0x0000000002f99c3a in runtime.fatalthrow.func1
    at /-S/contrib/go/_std_1.22/src/runtime/panic.go:1203
 8  0x0000000002fce48a in runtime.systemstack
    at /-S/contrib/go/_std_1.22/src/runtime/asm_amd64.s:509
 9  0x0000000002fce428 in runtime.systemstack_switch
    at /-S/contrib/go/_std_1.22/src/runtime/asm_amd64.s:474
10  0x0000000002f99b85 in runtime.fatalthrow
    at /-S/contrib/go/_std_1.22/src/runtime/panic.go:1192
11  0x0000000002f9981c in runtime.fatal
    at /-S/contrib/go/_std_1.22/src/runtime/panic.go:1042
12  0x0000000002f6f54e in runtime.mapassign
    at /-S/contrib/go/_std_1.22/src/runtime/map.go:596
13  0x0000000003ef3bc6 in github.com/jackc/pgx/v5/pgtype.(*Map).planEncodeDepth
    at /-S/vendor/github.com/jackc/pgx/v5/pgtype/pgtype.go:1254
14  0x0000000003ef99ed in github.com/jackc/pgx/v5/pgtype.(*Map).PlanEncode
    at /-S/vendor/github.com/jackc/pgx/v5/pgtype/pgtype.go:1234
15  0x0000000003ef99ed in github.com/jackc/pgx/v5/pgtype.(*Map).Encode
    at /-S/vendor/github.com/jackc/pgx/v5/pgtype/pgtype.go:2001
16  0x0000000003fe8e14 in github.com/jackc/pgx/v5.convertSimpleArgument
    at /-S/vendor/github.com/jackc/pgx/v5/values.go:17
17  0x0000000003fdfba6 in github.com/jackc/pgx/v5.(*Conn).sanitizeForSimpleQuery
    at /-S/vendor/github.com/jackc/pgx/v5/conn.go:1244
18  0x0000000003fdc06b in github.com/jackc/pgx/v5.(*Conn).Query
    at /-S/vendor/github.com/jackc/pgx/v5/conn.go:838
19  0x00000000040223ed in github.com/jackc/pgx/v5/stdlib.(*Conn).QueryContext
    at /-S/vendor/github.com/jackc/pgx/v5/stdlib/sql.go:493

...

oid = 0
format = 0

Possible solution

Protect map modification https://github.com/jackc/pgx/blob/04bcc0219dc3acf67f27e68decd6dffe97334779/pgtype/pgtype.go#L1235 with mutex.

Start in pgtype/pgtype.go around planEncodeDepth and the memoizedEncodePlans map modification identified in the issue. Reproduce concurrent simple-protocol queries, then verify the change under concurrent execution or the race detector. Done means concurrent queries no longer produce a concurrent map writes panic.