Player: allow setting mpv vf property for RTX Auto HDR / VSR support

[Aztup]

Expose vf property over IPC

This PR adds backend support for updating vf (mpv's video filter chain) from the frontend — enabling things like NVIDIA RTX Auto HDR and RTX VSR (Video Super Resolution) once the corresponding toggles land in stremio-web.

Concretely: adds Vf to the StrProp allowlist in stremio_player::communication so the web UI can send ["mpv-set-prop", ["vf", "..."]] through the existing IPC path. No behavior changes by default.

Example

Once this lands, the web UI can wire up RTX Auto HDR and RTX VSR toggles by sending the matching mpv-set-prop messages. For example, to enable both at once:

// RTX Auto HDR + RTX VSR (NVIDIA RTX 30/40-series, Windows HDR on)
["mpv-set-prop", ["hwdec", "d3d11va"]]
["mpv-set-prop", ["vf",    "d3d11vpp=scaling-mode=nvidia:scale=1:format=x2bgr10:nvidia-true-hdr"]]

Or just RTX VSR (upscaling only, no HDR conversion):

["mpv-set-prop", ["hwdec", "d3d11va"]]
["mpv-set-prop", ["vf",    "d3d11vpp=scaling-mode=nvidia:scale=1"]]

Toggling off:

["mpv-set-prop", ["hwdec", "auto"]]
["mpv-set-prop", ["vf",    ""]]

hwdec and vo were already on the allowlist; vf was the missing piece. The existing vo special-case in player.rs already auto-appends gpu-next (which d3d11vpp requires), so the web UI doesn't need to manage that.

Note: updating the bundled libmpv is required. The current bundle (v0.40.0-465) produces purple frames when the d3d11vpp filter is engaged in embedded mode; this is fixed in mpv v0.41+.

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AI was used to assist with this change (research, debugging, and drafting).

[kKaskak]

Ok but needs update in libmpv first

[Aztup]

Yea I didn't ship it with this pr because that might be considered unsafe

[kKaskak]

Yea I didn't ship it with this pr because that might be considered unsafe

We are going to upgrade it soon and then merge your pr