py_ext: fix CSV Writer

fix POU logic :
- SAVE is a BOOL
- invocation of py_eval on rising edge of SAVE
- remove save python argument

fix python:
- use no encoding for file open (python2)
- re-use detected dialect if any
- use no "rt+" and truncate since no need to re-sniff dialect for output file
- return "OK" instead of "#SUCCESS", preventing POU logic to ACK result
- support creating new line if writing just after last line
- support appending data on short rows

fix example:
- use a HMI:Button to trigger CSV write instead of HMI:Input +1
- reload CSVs on on each new CSV opened in file browser
- add display of CSV write output

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#ifndef BLOB_HPP

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#define BLOB_HPP

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#include <string>

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#include <filesystem>

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#include "md5.hpp"

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class Blob

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{

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public:

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    Blob(uint8_t *seedData, size_t seedLength);

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    ~Blob();

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    MD5::digest_t digest();

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    uint32_t appendChunk(uint8_t *data, size_t length);

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    uint32_t asFile(std::filesystem::path &filename);

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private:

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    MD5 md5;

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    std::FILE * m_file;

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    std::filesystem::path m_filename;

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};

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#endif // BLOB_HPP