Support `x` packet for binary memory read.

[daniel5151]

GDB recently (Dec 2024) gained support for this packet, via https://github.com/bminor/binutils-gdb/commit/e16e6389a7f1f6112868f470d7a001cb02e43d5d

Much like #82, which implemented x's sibling packet (X - for binary memory writes), this should be a simple, straightforward packet to add support for. It will simply hook into the existing Target-facing read_memory methods, and work as expected.

One other minor thing to keep in mind: we'll also want to add a new fn use_x_packet(&self) -> bool method to Target, in order to give space-constrained users the ability to opt-out of support for this packet, just as #82 added use_x_upcase_packet when it implemented support for X.

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Note that LLDB has already supported this packet for quite a while now. See https://lldb.llvm.org/resources/lldbgdbremote.html#x-binary-memory-read

Fortunately, GDB and LLDB share the exact same syntax and semantics for this packet, so no extra handling will be required to maintain compatibility between the two clients.

[dblnz]

I have spent some time on this, I'll prepare a PR in the coming days

[dblnz]

I got distracted and haven't prepared the PR yet, I'm planing for this end of the week

[daniel5151]

No worries. I'll be in Japan for vacation for the next 2 weeks, so its unlikely I'll be able to review it until I get back in ~mid December anyway.